This priest says there is no strong reason to doubt validity then seems to go on to strongly doubt it.
Fr. Peter Scott identifies "lesser reasons". Doubts can vary in strength.
That FAQ page is very old and Fr. Peter Scott is generally viewed as "old school".
Also, do you think men like des Lauriers and Carmona wouldn't know the situation and details of the consecrations a lot better than us?
I believe bishop de Castro Mayer said much the same thing - who would have known better than des Lauriers. [I see you posted this already]
Still, it would appear the old SSPX viewed the Thuc-line clergy as questionable.