Don't they have Lance-Sergeants in some regiments?
My dad was one in the Scots Guards. Wore 3 white stripes and was in reality a corporal. "Real" sergeants wore gold stripes.
Re retired rank. An admiral, KCB, moved to a Cornish village after he retired. He introduced himself at the pub, and the landlord asked him how he preferred to be addressed. He replied "Admiral, or Sir John - either is fine". He was somewhat taken aback on his next visit when a regular called out from the corner "Hello sailor!"