I misused the word law. Good to know. Makes it sound like adherance to guidelines by car manufacturers and shops are optional. Are they? Who enforces that they are practiced in the factory, and what happens if they decide not to practice them and manufacture cars any way they choose?
No one, not a single soul, or group or government agency "enforces" these guidelines, that is my point. It IS "optional" to follow them or not. The manufacturer is the most "concerned" for a lack of a better term because they don't want their cars out there repaired incorrectly where something could happen and their car is what would be splashed all over the news, not the repair shop who caused the problem.
There are all kinds of odd things like no manufacturer can "force" the consumer to use their parts for any reason, did you know that? They can't force the consumer to use their parts to uphold the warrantee. There have been many court fights over this one. There are some gray areas that I frankly can't sort out they get so complex but it is my understanding you could put some cheap aftermarket radiator in your 2012 Chevy during a collision repair and the GM has to honor any and all warrantees they have on the vehicle outside of the actual failure of the radiator. You could fill your 2012 Camaro with aftermarket parts and they can say NOTHING.
I print out these manufacturers guidelines nearly every single day to give to the techs in the shop. Every single welded on part, or suspension or brake part that gets changed, the tech gets the manufacturers guidelines and it is documented that they got it. I would say largely to C in the examples below. There are MANY times there is no guideline at all, in those cases we fall back on the "group" guidelines by groups like ICAR. I have to tell you, there is a LOT of conflicting opinions in these guidelines, a LOT. There are many cars that have simply none, not a damn thing other than a super general "Cut out a weld and put a new one when you weld in the new part" sort of guideline. Others like Mercedes have mind boggling guideline complete with things like panel gap gauges for proper panel fit.
There are just CRAZY out of this world ones like Toyota and some Chevy full frames that have a very strict repair guide line that basically says you can to zero repairs and to replace the frame for a little bend.
As a body shop or glass shop who wants to:
A. Wants to do the best job possible for their customer because damn it, it's the right thing to do.
B. Wants to do exactly what the manufacturer says because it will cover them if they end up in an investigation by the BAR (here in Ca.) or in court in a civil suit over some repairs they did that have failed in some way.
C. A combination of A and B.
But it is a choice, make no mistakes about it, it is a choice as there is no government agency who gives a crap about it. And that is the fact, if I am wrong I will be very gracious in my eating crow.