Studio Pottery bowl incised 'B'

Last one from me I promise (for the time being!) Bowl with impressed 'B' and was wondering if it was Bridgefoot Pottery and Ray Marshall? I have had Ray Marshall before but only pieces with his full signature...

Looks like a glaze test from 1974

The incised marks are probably a stoneware clay mix code, with the B being an alternative to A, C etc.

Looks like an incised B mark (I've edited the title line). Bridgefoot is an impressed B

I originally went with 'impressed' as it was so uniform to the eye but looking at the photos again there are marks it was incised as with the numbers so am assuming they must have been done with a stencil..... Which seems a bit of a 'faff' for a piece of studio pottery does it not? Especially in a recessed foot!

B 3,74
PS DL2/YB fe

So by B in March 74

Glaze test codes; maybe firing code too - I think the fe would be iron in the glaze.