make sure the .pk3 file is located in %quake3dir%\baseq3\ and nowhere else, no subfolders etc.
make sure your file is actually called <whatever>.pk3 and not <whatever>.pk3.zip or similar. turn off the options to hide well known file extensions in explorer.
You are wrong, but maybe you have some different map file. I checked it right now and there is a pro-nodm9.bsp file and it works with /cv map pro-nodm9 command
pro-nodm9 had an error fix near curved stairs that would make it so you wouldn't get stuck when trying to take the shortcut like in nodm9. It also I think had some minor item placement adjustments.
yeah that wasnt as much of issue in cpm since you would just ramp jump over the whole thing very easily, but in vq3 you were liable to fall down and get stuck.
and yeah there is minor item adjustment as well, such as removing the gl from the upper room, which is probably a very good thing for vq3 play.
for completeness there's also nodm9a included with the original which is a more extreme cpm remix.