Using different bikes and power meters for training (with AT enabled)

I’m sorry - I know this has been covered a bunch but I’m not sure where we stand now with AT and everything!

I have 3 bikes…basic MTB with no power meter, gravel bike with P2M crankset, and a road bike with a left side 4iiii PM. I’m using a Kickr Core for TR. Generally I think it’s best to have the same power inside and out, so using PowerMatch on the trainer would be ideal. I’m not sure what to do in my situation since I’d like to be able to each bike on the trainer.

Should I stick with the Kickr as the power source? I figure my P2M reads about 4% higher based on some non-scientific testing (recorded same ride on 2 devices) which makes sense given drivetrain losses. Wouldn’t this inflate my outdoor TSS?

I think back when they announced AT, they mentioned that using different bikes or equipment shouldn’t be an issue but I’m not sure what that means in practice.

Any tips are appreciated. Thanks!