Are PLCC Chips/Sockets always the same pitch?
Well, according to this article, yes:

"The PLCC utilizes a "J"-lead with pin spacings of 0.05" (1.27 mm)."

Which is confirmed by this page: the JEDEC standard for PLCC is "1.27mm (50mil) lead pitch".

I did a quick search at JEDEC but only found specification for trays and tubes.