I've already touched on this before but what I think is going on with the Nick multiverse is that you're not really seeing the Mirage Turtles or the FW Turtles, just general ideas of the major TMNT incarnations.
The main clue for this is that there only 10 dimensions, they're quite explicit about that on multiple occasions. Now if we were to add up any previously explicit dimension hopping or otherwise incompatiple depictions, we'd end up with something like this:
- Mirage
- Mark Martin's TMNT
- Hedden/McWeeny TMNT
- Mike Zulli TMNT
- Image TMNT
- Moo-Mesa
- Sakai Usagi
- The 79th Dimension of Null Time
- Mirage Super Turtles
- Fred Wolf TMNT
- FW Dimension X
- FW Video Games
- Archie Comics
- Archie Dimension X
- Live-Action TMNT
- The Next Mutation
- The 4Kids show
- 4Kids Dimension of 79th Dimension of Null Time
- Battle Nexus
- 4Kids Usagi
- SAINW Universe
- IDW TMNT
- GhostBusters
- Mutants in Manhattan
- Bopsteady universe
- IDW Dimension X
Incomplete but you get the idea, no way in hell only 10 realities can exist if we are to assume we're really seeing the original versions of the characters. Also, if the FW Turtles in the Nick show really are the FW Turtles, then you'd have to pretend none of these are canon:
So what I'm proposing instead is that the 10 Dimensions are not the past TMNT incarnations but rather some weird reflection of them and their most closely related material:
- Mirage
- Usagi
- Fred Wolf/Archie
- Live-Action/TNM/TMNT'07
- 4Kids/Dreamwave
- IDW
- Bayturtles
- Hell
- Dimension X