There are two basic strands left to us in the record of the Orkhomenian hero Erginos—one has him conquer Thebes only to be defeated in turn by Herakles (see Apd. 2.68-71; Paus. 9.37; D.S. 4.10; cf. Ades. Pap. 973.14-15) whereas another places him among the Argonauts (A.R. 1.186–189; Orphic Arg. 152-4), achieving a surprising victory during games on Lemnos (Pind. O4; Call. Fr. 699; cf. Mich. Apol. Prov. 7.95 for his proverbial status). According Ap. Rhodes and a fragment of the Historian Herodorus (43), this Erginos was from Miletus. This creates a bit of a quandary: where there two Erginoi? If not—which seems more likely—how did the hero become associated with both places?
The answer in part comes from the shadowy history of the people called the Minyans. Erginos does not seem to be a direct descendent of Minyas, but he was a king of Orkhomenos, a city called “Minyan” in Homer and elsewhere, in part to distinguish it from the Orchomenos in Arcadia. Fowler calls the Minyans the “magni nominis umbra of Greek Myth…[who] left enough traces to suggest that they were at one timea major presence both in mythologyand history. By the classicalperiod, however, they werea minor tribe, evicted from Orchomenos after the battle of Leuktra by their ancient enmies the Thebans (Paus. 4.27.10)” (2013, 191).
Their ethnonym is associated with the Argonauts (Schol. ad Pind. I1 79c) through settlement in Iolcus (Strabo 9.2.40; Schol ad. Ap. Rhodes 763-764), genealogical association with Athamas (a founder, according to Paus. 9.34.7) and Aiolos and shared geographical association with Thessaly and Thrace (Schol. in Pind. O14 5a3 and Schol ad Pind. P4 122). The civic-hero Erginos is listed as member of the Argonauts (Ap. Rhodes 1.113). In addition, they also show relationships with Ionian city-states which are likely influenced by colonization in the early archaic period: Pausanias records that one of the Ionian city-states (Phokaia) was settled by Phocians (7.3.10). As Pausanias also records, the ethnonym Phocaean extended in an early period all the way to Orhomenos (220.127.116.11). Although he writes that the Minyans settled Teôs (north of Miletus but south of Phokaia) Pausanias writes that the Minyans joined the Athenian expedition because they were related to Codrus; Codrus’ son Neileus took his contingent to Miletus. In conjunction with the colonization narratives, rulers of Orchomenos had associations with Argonautic myths: The eponymous Orchomenos died without a male heir and Klumenos, son of Presbon, son of Phrixus became king.
Panhellenic narratives like those of the Hesiodic Catalogue of Women integrate and subsume the Minyans by having the daughters of Minyas marry descendents of Aiolos (strengthening ties with Boeotia as well, Fowler 2013,192; cf. Paus. 9.36-37 and Schol.in Ap. Rhodes 1.230-3b). Here is the family tree of Erginos and Orkhomenos according to Pausanias:
Aiolos – Enarete [Aiolos – Ino (Thebes)]
Athamas – (Nephele) Almos
Phrixus – Chrysogeneia – Poseidon
So, as far as I can see, the likely reason that there are traditions for a Milesian and a Orkhomenian Erginos, both of whom could fairly be called Minyan, is that local narratives were carried by Minyans in their settlements to Ionia and connected as part of several layers of collective, Panhellenizing narratives into larger Greek traditions including the Argonauts, the Herakles cycle, and the Trojan War narratives. As the Minyans were subsumed into other regions and the importance of Orkhomenos declined, their heroic narratives were similarly subsumed and fragmented. One version of Erginos became associated with the Argonaut myth as part of a conceptual Minyan Diaspora; he was dissociated from the Boeotian Erginos as the Theban-centered Herakles tales rose into prominence.
Here are some of the more obscure sources.
Schol. in Pind. O14 5a3
“Of the Ancient-born Minyans”: the ancient race of the Minyans was from Minyas the Thessalian, a son of Poseidon, and the race(s) of the Argonauts came from him.”
BCDEQ παλαιγόνων Μινυᾶν: τὸ τῶν Μινυῶν γένος ἀρχαῖον ἀπὸ Μινυοῦ τοῦ Θεσσαλοῦ, Ποσειδῶνος υἱοῦ καὶ τοῦ γένους τῶν ᾿Αργοναυτῶν.
Schol. in Pind. O14 5d4
“From Minyas”: Minyas was the son of Kalliroê and Poseidon….And Minyas was the first to rule Orkhomenos.
EFQ ἀπὸ Μινύου. Μινύας δὲ ἐκ Καλλιρρόης τῆς ᾿Ωκεανοῦ καὶ Ποσειδῶνος.
BCEQ ὁ δὲ Μινύας πρῶτος ἦρξεν ᾿Ορχομενοῦ.
Schol ad Pind. P4 122
“After the Minyans sailed:” He speaks here of the Argonauts, since many of them trace their ancestry back to Minyas the son of Poseidon and Tritogeneia the daughter of Aiolos. So too Apollonios says : “Since most and the best of them claim to be from the blood of the daughters of Minyas.”
BDEGQ πλευσάντων Μινυᾶν: τῶν Μινυῶν· φησὶ δὲ τῶν ᾿Αργοναυτῶν, ὅτι οἱ πλείους αὐτῶν εἰς Μινύαν τὸν Ποσειδῶνος καὶ Τριτογενείας τῆς Αἰόλου τὸ γένος ἀνῆγον. καὶ ᾿Απολλώνιός φησιν (I 230)·
ἐπεὶ Μινύαο θυγατρῶν
οἱ πλεῖστοι καὶ ἄριστοι ἀφ’ αἵματος εὐχετόωντο.
Schol. ad Pind. I1 79c
“The Minyan retreat, he means Orkhomenos.” For he also calls Orkhomenos Minyan, since Minyas founded that city. They trace the lineage of that Minyas to Orkhomenos, as Pherecydes does, but some say that Orkhomenos is the son of Minyas and some say that both are the children of Eteokles, while Dionysios says Minyas is a child of Ares, Aristodemos makes him a son of Aleos and then he writes that the Argonauts are called Minyans for this reason.”
Μινύα δὲ μυχὸν τὸν ᾿Ορχομενὸν εἶπεν· οὗτος γὰρ λέγεται καὶ ᾿Ορχομενὸς Μινύειος· ταύτην γὰρ ἐνῴκησεν ὁ Μινύας. τοῦτον δὲ τὸν Μινύαν οἱ μὲν ᾿Ορχομενοῦ γενεαλογοῦσιν, ὡς Φερεκύδης (FHG I 92 M., I 102 J.), ἔνιοι δὲ ἔμπαλιν τὸν ᾿Ορχομενὸν Μινύου, ἔνιοι δὲ ἀμφοτέρους ᾿Ετεοκλέους γενεαλογοῦσι, Διονύσιος δὲ τὸν Μινύαν ῎Αρεος ἀναγράφει, ᾿Αριστόδημος δὲ ᾿Αλεοῦ τὸν Μινύαν, καὶ τοὺς ᾿Αργοναύτας δὲ Μινύας ἐντεῦθεν γράφει προσηγορεῦσθαι.
Schol.in Ap. Rhodes 1.230-3b
“Minyas had many daughters. For Jason, the son of Alkimedê, was the daughter of Klumenê, Minyas’ daughter. Stesichorus makes her Eteoklumenê whereas Pherecydes says Alkimedê, the daughter of Phulakos. Orkhomenos was the child of Isonoê the child of Danae and Zeus, which is where the city gets its name. Minyas was born from Orkhomenos and Hermippê, the daughter of Boiôtis, at least by name, he was actually the son of Poseidon. Minyas settled in Orkhomenos which is where the people get the name Minyans.
From Minyas and Klutodôrê came Presbôn and Periklumenê and Eteo and Athamas.klumenê, from Phanosura the daughter of Paion Minyas fathered Orkhomenos, Diokhthôndês
b ἐπεὶ Μινύαο θυγα<τρῶν>: ὁ γὰρ Μινύας πολλὰς εἶχεν θυγατέρας. καὶ γὰρ ὁ ᾿Ιάσων ᾿Αλκιμέδης ἐστὶ τῆς Κλυμένης τῆς Μινύου θυγατρός. Στησίχορος (fg 54 B. III 225) δὲ ᾿Ετεοκλυμένης φησίν, Φερεκύδης (3 fg 104 b J.) δὲ ᾿Αλκιμέδης τῆς Φυλάκου. ᾿Ισονόης δὲ τῆς Δαναοῦ καὶ Διὸς γίνεται ᾿Ορχομενός, ἀφ’ οὗ καὶ ἡ πόλις ᾿Ορχομενὸς καλεῖται· ᾿Ορχομενοῦ δὲ καὶ ῾Ερμίππης τῆς Βοιωτοῦ γίνεται Μινύας—ἐπίκλησιν, φύσει δὲ Ποσειδῶνος—, ὃς ᾤκει ἐν ᾿Ορχομενῷ, ἀφ’ οὗ ὁ λαὸς Μινύαι ἐκλήθησαν· ἐκ δὲ Μινύου καὶ Κλυτοδώρας γίνεται Πρέσβων καὶ Περικλυμένη καὶ ᾿Ετεοκλυμένη, ἐκ δὲ Φανοσύρας τῆς Παιῶνος καὶ Μινύου ᾿Ορχομενὸς καὶ Διοχθώνδης καὶ ᾿Αθάμας
Schol ad. Ap.Rhodes 763-764
“For the Minyans settled Iolkos, as Simonides says in his Summikta. This name takes precedents over Orchomenians. For many say that Athamas settled In Orchomenos.
᾿Ιώλκιος· τὴν γὰρ ᾿Ιωλκὸν Μινύαι ᾤκουν, ὥς φησι Σιμωνίδης ἐν Συμμίκτοις (8 fg 3 J.). δύναται δὲ καὶ ἀντὶ τοῦ ᾿Ορχομένιος· πολλοὶ γάρ φασιν ἐν ᾿Ορχομενῷ οἰκῆσαι τὸν ᾿Αθάμαντα.