It's a bigger stretch to go from "McPro" to assume Aviars in a thread about Roc3s.
And as for where the McPro's are suddenly coming from, just as Pbmercil says he's had them at least since 2015 World's (although we all know he's started using them since at least 2014). He has them because they get beat in quicker than his champion ones, and thus they can fly at slightly different lines (which of course, he is capable of consistently hitting). And he would have many back ups at World's in 2015 due to all those water hazards.
I think you referred to his "latest ITB", but that one was Feb 2015 when he last had 4 champ and 2 McPro (I mean of course, Roc3s here, and not Aviars). The actual "latest ITB" was actually in August (
https://www.reddit.com/r/discgolf/comments/3qlb3q/paul_mcbeth_2015_usdgc_in_the_bag/?) at USDGC where he has at least 4 McPros in his bag.
Pbmercil was referring to World's (
https://www.reddit.com/r/discgolf/comments/3gh7f7/mcbeths_worlds_itb/) around June/July 2015
where he mentioned he has 9 McPros (again, Roc3s, not Aviars here).