[Puma Cat]

Its a GAT, so...I think you have all the info you need.

I would very highly doubt that there any differences whatsoever between a lower SN and a higher number SN Series 1 GAT. That is simply not how production works. Any specific model has a set of engineering and parts specifications, and a BOM (Bill of Materials). Once you put a given model into "production" you want virtually all of them to be identical with respect to their engineering specification and BOM so that all customers can expect the same level of functionality and quality. The only reason an engineering change within a given series would be required would be due to a safety risk, regulatory compliance change, or a failure mode that was discovered post-launch that put the unit or end-user at some safety risk or failure to meet specification. This would be documented as part of the company's QA documentation as an ECO, or Engineering Change Order, and would likely result in a product recall. A good example would be the problems that Schiit encountered with the recent launch of the Sol turntable.

The Series 2 designation is where C-J made a specified change that resulted in a change in the GAT model range with respect to design, functionality, and possibly BOM that distinguishes that Series 2 from Series 1. This way C-J knows how to provide service and support units within each specific series.

Even the GAT S1 is arguably one of the best preamps ever built by anyone, ever...