If we didn't know JR was in China for part of January, would we all assume from JP's update that when he mentions "our first month", he'd have meant the WHOLE band, drummer included?
Knowing JR wasn't there the whole time, and possibly JLB, we can't be too sure if the drummer was present, but there are plenty of strong points for each side of this. I think they're being smart not revealing whether or not their new drummer is present because then someone would definitely be scoping out the studio by now.
I can picture it - to sneak out the new drummer, the band give him a jacket and pizza-bag and hat to walk out of the studio with, and anyone watching would think it was just someone delivering pizza! Genius!
-Marc.