Because the standards by which nav lights are built is not published in the COLREG's it is in the CFR (Code of Federal Regulations). You, as a used boat owner, are NOT required to have "certified" nav lights or install them UNLESS you are a boat builder. If you buy a new boat in the US it WILL have certified nav lights of the builder broke federal regulations.
If you are a builder you must use USCG/ABYC A-16 nav lights properly installed and placed for proper visibility. All USCG certified or ABYC A-16 lights will meet the minimum standards as set forth by the CFR. This is what labs like IMANNA use when testing nav lights to USCG/CFR nav light standards..
Ah, thanks for that MaineSail.