One answer was that the glue including mineral and whatever factored in, but that doesn't make sense to me, in that the aged glue itself would not necessarily record when the organism was deposited.
True, in the strictest sense. But if that leaf hasn't had its original tissues replaced by minerals in, say, 50,000 years or so,
there won't be a fossil left for us to see (unless it is perhaps a cast) after a few million years. A 50,000-year error in a date of 50,000,000 years is the same size of error as being an hour off in something that you remember from 41 days ago - early February. Not a deal-killer in the question, "when did this leaf fall." Patticularly when the leaf is of a sort that has never been found on a modern tree.