Standardized extracts: inconsistent strength?

[bcubed]

My lizard recently purchased 1gr. 17X from a reputable head shop. He'd already consumed about 1/3 of the product on several occasions, and it seemed to be reasonably close to advertised strength: he'd guess it 10-15X if he didn't have any other reference but effect.

However, recently he smoked 1 toke (maybe 0.05-0.1gr?), which was (for him) a very small dose. Rather than the modest "attitude adjustment" he was expecting, he experienced the most profound effects ever (solid "V" level)! If he guessed at strength here, he'd say 100X or so.

What I wonder is: has anyone noticed strength inconsistency within the same batch of extract? Since strength is almost impossible to guage outside of effects or an acetone wash (although strong Salvia seems to taste more bitter), this has me wondering. Salvia is such an inconsistent drug, though, that maybe it's just "one of those things."