Here is my 3870.
Marked with patent 2,977,824 granted to SK powerhouse ratchet designer T. Rueb (who also invented and improved the SK round head) on April 4, 1961.
This one isn't the prettiest with plating wear but works great, she's not afraid of getting her hands dirty either...finished a brake job on my Accord after my brand new Proto XL ratchet I was using broke.
I think I read somewhere that after Symington Wayne bought SK and Lectrolite in 1962, there was a delay to retool production lines to stamp tools SK Wayne. This delay was 1 or 2 years.
The gentleman I bought it off of purchased it new in the spring of 1963. So who knows if it was a leftover from original SK, or an SK Wayne made with the old tooling. I've only seen a couple other examples like this leading me to believe there aren't many. Idk if I'd say rarest Roto...
Probably the rarest Roto I've seen was a JC Penney stamped version in a red/translucent plastic pouch (from the brief period of time SK made tools for Penneys). It came with something else small, maybe spark plug sockets or an extension. Someone over on the journal had one, it was NOS in pouch and very drool worthy.