NBOMe was super popular in the early 2010s. I'd be willing to bet that on my college campus 90+% of "LSD" was some sort of NBOMe during that time.

No idea what's going on nowadays but plenty of gray market LSD analogous will test positive as LSD (Al-LAD, Pro-LAD, Eth-LAD, 1P-LSD, idk what else is available now). I wouldn't be shocked if people get those without realizing.