ROB, Reb Mshe’s Teshuva says if someone didn’t accept to keep the full slate of mitzvos, then there is no geirus. He repeats this point in the next few teshuvos. What is also indisputable is that we don’t lechatchila accept geirim whom we suspect of converting for ulterior motives. That is a befeirush gemara, not some diyuk. You keep avoiding this point, but it keeps coming back.
So yes, we want to know that the person in question did a full kabbalas hamitzvos. Kabbalas hamitzvos is a timeless principle. If we know that they did a full kabbalas hamitzvos, and they slide, that is a machlokes the Taz and Prisha. But we need to know that first. If we don’t see the convert living a Jewish Orthodox lifestyle, then anan sahadi he/she never meant to . It’s black and white- not sure how this can be distorted into being an “expired” teshuva.