STC holder permissions, and "only dealer installations allowed"

I find it a “stretch” to argue that

• you need installation data
• it needs the be current
• it is available on the official mfg website
• that website login is issued only to the mfg’s official dealers
• the STC is therefore valid only for dealer installations

I accept the first two points (well, to the extent of the equipment actually going in, e.g. does installing a 2004 GTX330 need the latest (2017, say) IM and the 2004 IM would not be legal?) but to argue the rest would imply that any existence of the current data away from the mfg website is somehow not a “real existence”

There is an argument, in other scenarios, that any printed copy is “uncontrolled” and cannot be used for anything real. But an installer may be working from a printout and not have a laptop running in the plane he is working on. So the installation would be illegal. And what if a dealer gives someone a copy of the PDF?

It quickly gets totally absurd.

Also the reality is that a huge amount of installations are done around the world by non dealers; are all these illegal?