Then there is a bug in the count of CHD games in MAME. There is no other explanation. I don't see any mistake here...
Attached is the list of 1065 games using CHD files. I can't attach a txt file or zip file here for some reason. The number 1074 is wrong. Please give me the 9 games you think I'm missing and I'm happy to show you they don't use any CHD file.
Maybe it are clones (without "disk" tag) that have a parent with "disk" tag(s) and the clone uses the CHD files of that parent? Investigating now...
Can a MAME developer confirm my last thought is a possibility?