No evidence to support such a claim.
While I will acknowledge that there might be some interior changes from ship to ship regardless of class, I think SF builds all of their vessel classes from one set of blueprints.
So essentially speaking, the design itself will be identical when it comes to class.
The only changes you might possibly expect are some interior changes and fine-tuning of power generators (and whatnot).
True, but it's pretty much common sense... in that this is something that every single real-world application you can find shows exactly this as being the case.
One of the teams where I'm working is doing a design revision for the next-generation version of the C-130 transport. They're working on just one small subsystem, mind you. The thing is, they need to put their devices into every ship in the fleet, and so far no two C-130 airframes have been close enough to allow a "single solution." Basically, the mechanism (which I wont' go into here) is going to require a CUSTOMIZED INSTALLATION for each and every aircraft. Most parts can be common... but it's not just a matter of shipping a "box set" of parts to the field and have them be installed... nope. A set of measurements need to be taken first, then the custom installation hardware is fabricated off of those measurements. THEN the hardware can be installed... not before.
Weird? Nah... it's totally commonplace. And the more complicated the hardware you're dealing with... in terms of part-count, assembly steps and processes, or simply tolerance stack-ups... the more common this is.
A Galaxy-class is a VERY complicated piece of hardware.