I don't know why some had a full stop and others differed , apart from maybe a change in manufacturer or a Wartime shortage of braid. I do know that during WWII, Royal Naval personnel were forbidden to wear the ship's name on their cap, for security reasons, so each 'tally' normally only had 'H.M.S.' on it. There were some who were allowed to have 'destroyer' or 'minesweeper' on it, but not the ship's name.