When adding repeatedly with ZIP/U, the size of the .zip archive may vary — which I can work with.

The size may become larger than the total size of the added files — which I don't like so much.
In one case (the .zip archive is a "backup" of a directory, i-e the list of files doesn't change much nor does their size):
- the .zip archive was 258,735 bytes large,
- after ZIP/U, the .zip archive is 876,470 bytes large, although the files themselves amount for 279,394 bytes on disk.
ZIP/V and IZArc give no clue, one simply sees the expected list of files, with size and compression rate.

When I ran some tests, I tried to keep only the files with a name starting with 'A'.
ZIP /D myzip [B-Z]*
starts deleting files in ASCII order (starting at 'B'), but at some place (about 'Q' or 'S' depending on the exact run) deletes the .zip archive itself. Running
ZIP /D myzip B*
and then for each letter up to 'Z', correctly leaves the .zip archive with the 4 files starting with 'A'.