[maryz]

yet it's the source of Catholic and Orthodox belief in Mary's perpetual virginity

I don't see how you can be sure the belief didn't precede the Protoevangelium and so ended up being included in it.

[kosta50]

I don't see how you can be sure the belief didn't precede the Protoevangelium and so ended up being included in it

I didn't say the belief didn't precede the Protoevangelium. The Infancy Gospel is used as written evidence of such tradition.