Spear & Jackson Tenon? Dovetail? Back?

I picked this one up yesterday, cleaned it up a bit, and took some photos. I've never acquired a Spear and Jackson before, then yesterday I buy two saws -- this one and a Lloyd Davies, which I believe is also a S&J (also a tenon, dovetail, or backsaw). Here are the specifics on this one:

-- 12", 13 PPI, Spear & Jackson SHEFFIELD on the spine, steel spine, split nuts, I believe original handle (no extra holes), blade thickness = 0.025 in

The handle was painted dark red, so I stripped that off. It looks like part of the handle had been burned at some point (maybe that's why they painted it).

Here are my questions:

1) According to my "Hand-Saw Makers of North America" book, it appears to show S&J beginning in 1915. If so, then why the split nuts?
2) Should there be an etch? (none is visible)
3) Every one I see on eBay has a brass spine, but mine is steel -- is mine the exception, or maybe a later model?
4) Curious why the SHEFFIELD stamp is slightly off-center from the Spear & Jackson stamp above it (others I've seen have SHEFFIELD centered)
5) What type of saw is this -- Back, Tenon, Dovetail?
6) Any idea on age?

I'm posting this on Backsaw.net as well.

Regards,
Dave

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