I've seen Jane's Strategic Weapons Systems label them both as the same weapon (53T6 and PRS-1). But Jane's has always been notoriously inaccurate when you're dealing with FSU missiles and land-based radar systems (they refer to the S-300PM-1 EW radar, for example, as TOMB STONE when it is actually the 64N6 BIG BIRD).

Also, I've got an electronic copy of the Fakel OKB's in-house history. It describes the S-225 as being a point defense system to defend targets against one or two ICBMs. Kinda like an S-300V on steroids, really. Unfortunately it pretty much ignores such things like launchers, radars, and other OKB's missiles like the A-135's 53T6. But there's a lot of very good stuff on all of Fakel's products. They've even got photos of the test launches of the 9M96 missiles for the S-300PM-2 and S-400, as well as loads of images of the V-1000, and the M-2 GUIDELINE, the naval SA-2 variant.

Barring the direct historical document, I'll trust Podvig, given that he's been researching everything Russian and strategic for a very long time. His book is excellent, if you don't have a copy you should track one down. At around $60, it's a great bargain I think. Plus, it's huge.