There is no reason a priori to doubt the validity of the Novus Ordo Baptisms because the essentials have not changed (this applies to Penance and Matrimony as well). The doubt only concerns the other 4 new Sacraments: Confirmation, Eucharist, Extreme Unction, and Orders.
You wish, but it is the case, nevertheless.
The new rite of baptism does not ensure that water is poured on the head, which is cause to doubt, unless and until investigation gives positive evidence of validity.
As well, a separate cause, the Novus Ordo are inclined to be negligent and experimental, this alone is enough to consider it doubtful, until investigation give positive evidence of validity. This is the same reason all Protestant rites are considered doubtful, even if the sect uses the traditional Catholic rite of baptism. It's on the books.