So I've been noticing on some cars descriptions the creators are telling me to install a car say "police4" into patchday11 but I don't have a police4 in patchday 11. If I install it into patchday 11 and don't find which directory has the police4, will it still work or are my cars in different areas for some reason?

Whatever file you were uploading it must be a tad old.  At the time patchday 11 was the highest patchday,   When you install vehicle files as a general rule of thumb the game loads the files from the highest patchday first.  So always choose the latest patchday when you add vehicles etc....   so for instance-  if you add police 4 to the latest patchday that will override the original police 4 file.   If you took out the vehicle you just added from latest patchday the game would just load the original file again.   Make sense?

 

and you are using a mods folder correct?

Yes I'm using a mods folder. But i've been searching for the original files in openiv and it was taking forever so I was curious if I put the new files into the latest patchday which is 20 for me if it would override the ones in say patchday 3

Yes that is correct