Even then, I often board with my coworkers who have higher status than me. If we're sitting next to each other and he's in group 2 but I'm in group 6, I'll generally board with him anyway and no one seems to care.
The system may not be aware of something like boarding groups, especially since every airline does them differently.
It's entirely possible that the "check" is "is this boarding pass checksum valid.", especially given the stories of boarding wrong flights - it doesn't even flash red for "this is not the right pass for this flight".
Depends on an airline and maybe even airport, I guess.
Anecdotally, last time I was flying on a business to Germany with Lufthansa, my cow-orker did the Internet check-in for me without me knowing, and printed out the boarding passes. I later did the check-in for myself again, and picked a different seat. At the airport, the friend gave me the boarding pass he printed (with the old seat number), and so I thought, let's check if it still works on the scanners. I scanned it when boarding, and the scanner threw up an error that the seat on the pass does not agree with the one that's actually booked. I pulled the up-to-date boardin pass on my phone and continued on my way - but it seems that there is some actual checking being done, not just CRC.
I have my friends do this when they travel with me. I tell them that if the gate agent says something, tell them you have a peanut allergy and need extra time to wipe the seat down. That line has worked every time.
"tell them you have a peanut allergy and need extra time to wipe the seat"
Another often overlooked travel tip is that you can park in handicap spaces to save walking 10 extra feet.
That's not a life hack thats deliberately lying to someone whose job requires them to accommodate you to sometimes great degrees. Like not serving peanuts to those around you.
It's entirely possible that the "check" is "is this boarding pass checksum valid.", especially given the stories of boarding wrong flights - it doesn't even flash red for "this is not the right pass for this flight".