I'm pretty sure we aren't going to agree on this one!!!Nash is in the Tas. Team Of The Century, & is a Legend in the Tas. Hall Of Fame!
We have no record of Nash playing any adult AF in Melb. before the family moved to Tas. -& your Trove searches to find such experiences have not been fruitful. And you did provide Trove references of the Nash brothers playing in an adult team at Parattah in Tas. in 1929, where their father had his hotel.
No Melb. Clubs had any interest in recruiting L.Nash before his move to Tas. It is very reasonable for Tas., & others, to claim he was devel. in Tas. There is no necessity for State Of Origin criteria.
Ivor Warne-Smith is in the Tasmanian Team Of The Century and is a Legend in it's Hall Of Fame despite not being a "genuine" Tasmanian as well, and the likes of Andy Bennett, Roy Cazaly, John Devine, Stuart Spencer and most likely a few others (who are not genuine Tas. products) are in the HoF as well.
Tim Evans (a real Tasmanian!) is in the Tas. Hall Of Fame and the SA HoF as well. Of course he belongs in both! Laurie Nash, and people from other states who made a real contribution to the game in Tasmania, or at least spent a bit of time there and made a name for themselves elsewhere, belong in the state's HoF too.
As I've already quite reasonably suggested, Victoria can take credit for developing Nash. He was born and bred there, came from a football family and had probably been playing the game for a decade or more as a junior when he moved to the southern state. He was about 19 when he moved, hardly comparable to e.g. Nick Riewoldt moving from Tas. to Qld. when around 9 or so. It's just not particularly important that he hadn't played at an adult level in his home state (there may well be a decent reason for that as suggested on his Wikipedia page), and while my Trove searching skills are of the highest order, the fact that nothing has shown up that says senior Vic. clubs were chasing him doesn't mean it didn't happen!!
I'm happy to keep mentioning a players' State Of Origin in a case like this, because it's the key point of the whole discussion! Where a player spent his (football) formative years is where they belong. In the case of Laurie Nash that of course is Victoria. Very soon after he started playing at a reasonable level in Tasmania he was deemed good enough to play representative football; his one season at Parattah and then playing under the great Roy Cazaly for just a few games can hardly have transformed him from "undeveloped" into someone capable of starring against the country's best players in a national carnival, unless he had a pretty decent idea of how to play the game in the first place!!