Retcon, no. Author being deceptive and vague, yes. He very intentionally said "if Aizen has ten vastorodes we're fucked" and then cut to a scene of Aizen saying "look at my 20 arrancar".
Of those arrancar, 4 MIGHT be vastorodes, and even they aren't confirmed yet.
Bleach has done retcons before (making Shawlong and Co fraccion after the fact, Isshin not being beaten by the hollow in the intro, a couple other minor things) but that wasn't one of them.