I would imagine that some are prevented by the spousal exit clause?
Some people, for whatever reason (religion, finances, whatever) never divorce, even if they permanently separate.
In these circumstances, if the wife won’t agree to be in a lesbian marriage she never signed up for (or the husband won’t agree to a gay marriage he never signed up for) a GRC is unobtainable. The marriage must be dissolved if the spouse does not officially agree.
The proposed new style GRC doesn’t ask for spousal permission.
Seven Hex has said he doesn’t think historical birth records should be retrospectively tampered with and thus has never wanted a GRC. He wrote a blog about it, might still be online somewhere.
Interestingly, Adam Graham is legally married but had done a runner, leaving his wife (very short marriage) unable to serve divorce papers.
Being married would’ve prevented Graham from changing his birth certificate, so even if he’d managed to get to two years of gas bills addressed to ‘Annie’ or ‘Isla’ AND get his paperwork signed off by the GRC panel before the rape charge became a conviction.
He would’ve gotten stuck at the ‘interim GRC’ stage, due to the spousal clause.