Suspect that COCKCHAFER, as a naval auxiliary, was not in Lloyd's Register when LR/IMO unique numbers began, so would have received a number later - perhaps in 2001, though possibly earlier. Some of these were given numbers in the 4xxxxxx series; others, mainly yachts, in 1xxxxxx series. Since 1991 allocated numbers have been entirely without "meaning" - they are just a number.