If you say someone committed murder with zero evidence to back it up it's wrong-- at that time-- even if evidence ends up coming out. You still had no basis for such a serious accusation and would still be irresponsible to throw the accusation around as "true".

Sometimes people make unfounded guesses based on little/no evidence. Just because it turns out to be correct doesn't mean those people were any more justified-- at that time-- in their unfounded accusations.

Of course a person is now justified, with evidence available, to make these claims. It doesn't mean those who made them baselessly out of suspicion and guesses any less irrational for doing so before there was evidence. Making unfounded accusations doesn't retroactively turn an irrational accusation into a reasonable one just because it turns out to be true.

It's also worth noting that this is still unproven: it doesn't look good for China, but there's nothing definitive yet.