"There is no plausible path" are just words, not a fact.

Moderna had more cultural status in the period we're worried about. More affluent, PMC women could have been more likely to seek out Moderna and more trusting of The Science and likely to get injected while early in pregnancy. Less affluent women more likely to accept Pfizer and to wait until they were pressured by obgyn. The 'preliminary findings' cohort was overwhelmingly healthcare workers so these biases wouldn't apply, but afterward they would.

And once again it's impossible for a disparate fertility impact, if there was one, not to have affected the periconception cohort makeup in some additive fashion.