There's a plate on the drivers door that has your factory wheel information, isn't there? I've "lost mine". Thus, if I ever get asked, my stock wheel width was 6.5" - or 7", etc. Whatever's convenient.
The upside of having a car like ours is the cops hardly ever have an idea of what's legal on a pintara. That, and no cop is ever going to go - "hang on, that wheel is 8", not 7.8"". Basically they have better things to do. When all else fails - swap to stocks, clear the defect, swap back.