So when dry vaporizing we are basically doing the same thing...... except much hotter - we're talking closer to 150c and hotter to release the vapor from the herb.
In fact, we use different temperatures (between 150c and 220C) to release different medical benefits from the flower (low temps around 150C for more uplifting cerebral effects, and high temps over 200C for more pain relief and sedation).
Recently picked up a 1g preroll of cannabis from the dispensary and left it in my car for a week (ambient temps around 41°). When I went to smoke it, it smelled the same and looked the same (was in a sealed plastic container) but it had no effect whatsoever. Does THC degrade at high ambient temps?
Yes something will start to degrade at 40c, but what you experienced is not that......
Fun story for you:
I had a similar experience in Las Vegas. While attending a CHAMPS trade show (420 industry b2b event) in Las Vegas, the different recreational dispensaries were giving away free pre-rolls and large discounts to any customer who had a CHAMPS badge from the show. Since I don't combust (dry vaporizing only), I took the free pre-roll from one dispensary and emptied the shake. Then I cooked it in my dry herbal vaporizer.
Except I got literally zero vapor!!!! I honestly thought my vaporizer was broken. Until I reloaded the device with some fresh top-shelf flower and boom, I got a ton of vapor. As it turns out, the dispensary I visited was extracting all concentrate from the herb to sell wax concentrate to customers. The leftover shake from that process was put into pre-rolls and sold as cheap 1g smokes despite the fact that they contained essentially zero active compounds.
To the average smoker, its cheap and it produces smoke (plus the combustion creates a toxic cocktail of carcinogenics and carbon monoxide can yield temporary euphoric and sedative affects which fools many ents). But with my dry herbal vaporizer I immediately noticed the problem.
So to answer your question, no I highly doubt that leaving a pre-roll in a car at 40c would cook off ALL active compounds. Maybe some low-temp terps, but not everything.
Does that dispensary also sell concentrates? It's very likely they are trying to double-dip by selling both the concentrates and the trash shake as pre-rolls so they can increase profits. And I'm sure the local government doesn't care that they're misleading customers - because they're still earning tax revenue and all that jazz.
If you don't believe me, it would be really easy to test with a dry herbal vaporizer - put some of that pre-roll into a dry vaporizer set to 200C and start cooking - do you see much vapor production? Or does the device produce practically zero vapor? That'd be because there are no active compounds left to extract at those temps.
Just my $0.02