I have a pre-WW2 clubman frame that is far too light for 531 and is probably A&P Kromo.
I think TI killed off the bicycle tubes line to avoid competing with the Reynolds brand although, as we now know, chromoly had more potential than mang-moly. To be fair, chromoly only really came into its own when decent welded frames took over in the MTB boom. Americans had always welded, not brazed, high volume bike frames, but MTBs showed it could be done nicely.