There seems to be a lot of confusion about the different counterweights and flywheels (stock and aftermarket) for the rotary engine, so I’ll attempt to clear some of that up here.
Rotary engines have a balanced rotating assembly just like any other engine. This involves the e-shaft (which doesn’t require any external balance in itself), both rotors, a front counterweight, and a rear counterweight. There were different weights of rotors through the years, so the balance is different for each of these different engines. The front counterweight is under the front cover, and should never be changed unless a custom engine is built using different rotors. The rear counterweight can take one of 2 forms; it can be a flywheel with the counterweight integrated into it (cast) or it can be an automatic counterweight with the 6 bolt pattern for the ringgear to bolt onto. All stock flywheels fit a specific year and model of engine, and are numbered, and all have the counterweight for that engine cast into them.
Note that for 1st generation cars and older rotary vehicles, 12a or 13b, only one DIAMETER of flywheel is used, the 205mm nonturbo version. Between various years of 12a and 13b the COUNTERWEIGHTING changed to reflect the weight of the rotors inside the engine, so there are several different flywheels for the different engines.
For 2nd generation cars, there are 2 DIAMETER flywheels used…the 205mm nonturbo, and the 225mm turbo. In addition, the weights of the rotors changed between 88 and 89 (series 4 and series 5) so for each of the 2 diameters, there are 2 different counterweights, for a total of 4 unique flywheels for 2nd gen engines.
For 3rd generation cars, there is only one stock flywheel, in the larger 225mm turbo diameter, since there was only one engine available stock.