Hmm interesting, do you think Mary might still be the only surviving child then for Henry and Catherine? I'm working under the assumption that Arthur does still die as in otl.
I alluded to this earlier, but there's a theory that Henry VIII had a rare Kell Positive Blood Type (90% don't have it) which makes it hard to get living children from Kell negative wives (especially after the first pregnancy- Elizabeth, Edward and Fitzroy all being the result of the woman's first pregnancy with Henry). As far as I can make out, if they experience multiple pregnancies with Kell Positive foetuses, a Kell negative mother will develop antigens that attack the foetus' Kell positive red blood cells as 'foreign' and result in miscarriage.
If that hypothesis is correct (and I'm not into genetics so I can't offer much insight here) then Henry and Katherine were doomed to have childbearing issues and potentially only have a single child (whether that child is Mary or from one of their other pregnancies is mostly dumb luck about whether the foetus inherits Kell Positive from Henry).