I'd literally bang my head on a wall if I went through that much trouble for a tricky achievement like that and it ended up not working... I doubt the fact that you formed Scandinavia from Norway blocked the achievement though.
It is, look at the code above. The last bit indicates there can't be any naval supplies owned that are not owned by tag=NOR.
There should a bit under it that says something like
Code:
OR
NOT = { owned_by = SCA }
Much in the same way One Night In Paris requires you to have tag=ENG or tag=GBR (which I guess means if you started as England, cultural shifted and formed, say... Russia, then took Paris, you wouldn't get the achievement. Also, you have to start as England so you can't form GBR as Scotland and get the achievement).
Hope they change it, it seems kinda arbitrary, especially given that every other achievement like this isn't hampered by "can't form the likely formable nation" rule. Sweden can safely form Scandinavia, Poland can safely form the Commonwealth, England can safely form Great Britain, the Irish minors can safely form Ireland...
But if Norway forms its likely formable nation, *poof*, you're out of luck. It seems like the game should at least check:
1. If you started as Norway
2. If you're currently either Norway or Scandinavia
Either that, or all of the other achievements should be changed to have the same rule to keep them all in line with one another... but that wouldn't be fun for anyone.