Missing Mb


iBook G4 running 10.4.2

Can you help with the following puzzle please?
My 'Users' folder is held in a separate 5Gb partition of the hard disc called DAD (DAta Disc). Get info shows that I have used 3.74 Gb of DAD but a Get Info on the 'Users' directory shows its size to be 2.82 Gb some 920 Mb less.

Use of the command 'ls -hla' at the Terminal enables me to identify and find the size of the invisible siblings of 'Users' (and their descendants) but these amount to only some 90 Mb. I must be missing something obvious here but can you tell me what could be using the remaining 830 Mb? TIA