It’s great that you ask a question and only one of the 4 posters actually discusses it.
Regarding your question….
As a longtime collector of t206s, especially rare backs, I can state with confidence that there is zero premium associated with an SC 350-460, 25 back. I agree with Sonny completely (who btw knows more about rare back pricing than anyone).
The only piedmont and sweet cap backs that get a premium are both piedmont - the factory 42 and 11 for players in the piedmont 350 back (the elite 11). Otherwise, all sweet cap and piedmont variations are common and worth the same as far as backs go.
Maybe, sometimes, you can get a small premium for series 150, bc it’s 1909 and earliest, and, in my experience, the sweet cap 350, 25 can be super tough, so people going for a back run may pay up a bit for that. The problem with the sweet cap 350-460, specifically, is that it is a very common back with only factory differences to distinguish. If you took away factories, I think it is most common, and, aside from the piedmont 42, I really don’t think people give a hoot about the factory number.
All that said, that matty is a blazer. You should certainly get a premium for eye appeal (but not the back)