I have noticed Indica tends to be lighter in color when it is done and tastes like popcorn. Sativa tends to last until its much darker before becoming popcorn tasting. When milking a bottle the vapor tends to vanish when the popcorn flavor arrives.
Yeah, losing the stickiness is a better indicator to me.
Not all vaporizers/temp settings/etc. produce that flavor and some will do it even before the load is completely done. If I try to dump it and some holds onto the bowl though, I can still get some extra vapor out of that before it stops holding on falls out too.
Still, in many cases the burnt popcorn smell/flavor are a good indication that it’s at least done enough for me to dump it, so I don’t think we should ignore it as one way to judge what’s left in a bowl.