"Local slug tries to guess where on the '87 timeline the '12 crossover exists with the power of Wikipedia"
Ok! So, this is specifically the Wormquake Part 2 cameo and the episode 'Trans-Dimensional Turtles'. I can make no claims as to the other crossovers.
Evidence to narrow it down:
Rob Paulson voices Raph- seasons 1-9
Red Sky/ Gets dark- seasons 8-10
Krang is in play- seasons 2-8
Mikey fights with nunchaku- seasons 1-3
This evidence limits the potential range to after season 1 but before season 4.
As the Usagi Yojimbo crossover takes place in season 3 and the Technodome is sent to Dimension X in the finale of that very season, I would like to hypothesize that the episode 'Trans-Dimensional Turtles' and the cameo in 'Wormquake Part 2' occur between seasons 3 and 4 of the 1987 TMNT.
**Upon further inspection, it should be noted that Dimension X is a place where time operates differently and the Casey cameo in Wormquake Part 1 could be spying in on the future after he and April have actually met/ sometime between season 5 and 7???**
Shouting into the Void: Can anyone who has actually seen this show confirm or deny my conclusion/ evidence?