You are correct - there was such an update. Apple only did it that once, and it was basically an emergency release to fix serious bugs in 7.5.3 (I think), similar to the 10.2.8 fiasco.MacNut said:I could be wrong but I thought that system 7 had a 4 number update like that.
EDIT: looks like xsedrinam beat me to it. What a cool name, xsedrinam