I believe this was a Stanley Sheffield project, under the (Stanley USA) brand Sweetheart. Plane bodies being made by Stanley Mexico and the steel for blades by Stanley in their Sheff works. Assembly, packing etc in Sheffield. As well as smoothing planes there was at least one type of shoulder plane (no92), a low angle block plane and a set of socket chisels looking like Stanley's from the '40s.
I'm not mad on these small socket chisels but they're obviously popular as copied (more expensively) by Lie Nielson and others and I confess to owning a couple of these modern Sweethearts and a part set of similar Marples from about 1950??
Strangely, the UK wholesaler JTF had a ton of spare blades for the Sweethearts about 10 years ago, for pence. I bought some just because cheap -- they are of A2 steel, finely ground, 3mm thick, and with a sharp 25deg bevel.
The packaging is dated 2008 and the sell off of blades was about 2011? so looks like a quickly aborted project and I guess product like the chisels still available 'new' is long gone from the current catalogue. Shame, because they were a good price and a quality product even if a few details (see other posts) could have been better.