Taking info from some books by frank and rosenthal, the actual % of THC could be higher because less of it has a chance to be degraded by light/heat/oxy, however the THC + degraded substances could easily be the same. Mel Frank offers a lot of evidence suggesting that bud matter contains all its THC when first developing new growth, and that after being created the tissue will begin degrading, basically that all other things equal, new growth will have a higher THC content, and older growth will have a higher CBD content. However, it has been shown that THC levels fluctuate throughout the day/night, so I'm not sure how that jives with the proceeding theory, and if fluctuating throughout the day I'm not sure how accuratley you could gage %'s based on time in flower.
Anyway, not sure anyone is going to be able to give you a definitive answer. I hope the info help you formulate a more educated guess/solution!