BSA and Enfield were parent companies. I've never seen a publication covering Nortons and if it existed, it would almost certainly have had to be under the name of R.T. Shelley but they seem to have published little and perhaps deliberately kept the relationship between the group companies rather vague.
Ian, we're still finding odd batches of Nortons including the Australian contract that didn't seem to have been documented so there may have been more than we thought but I don't think there can be any doubt that Norton's claim must have included the pre-war War Office and India Office contracts.