Air Ministry lens were made by various manufacturers, so while Ross might have managed a project the actual lens could have been sub-contracted & made by Dallmeyer, Wray, Aldis etc.
Ross were given control of the Carl Zeiss factory in Mill Hill, London after the outbreak of WWI which made binoculars as well as some lenses, and seem to have had the lions share of AM contracts after that. They were the UK manufacturers of Zeiss & Goerz lenses prior to WWI.
Ian