Cheers Rob. Yes, I think the bracket numbering with rifle serial started just post-war.
I was moved to get off my posterior this evening & do a quick 'straw poll' of about a dozen brackets that were to hand, approximately half each of Rose Brothers & Dalgleish. ALL of the Dalgleish brackets bore cradle clamps with letter suffixes, & NONE of the Rose Brothers (which bore just numbers alone). Now, I've been collecting this stuff for a number of decades, but it took till tonight for me to look at them systematically..........though of course I'm aware that twelve is hardly a statistically significant number to start generalising, but it'd be interesting to see if others follow this trend. I excluded one bracket from the L42 era that had clearly been re-stamped (though it did follow suit anyway!).