Please check my calculations

So I brewed a batch of DFH 60 min IPA last night with my newly sewn BIAB. I'm calculating my efficiency and found a discrepency between the pre-boil and post-boil efficiencies. Let me know if you see anything that looks funny

12lbs American 2-rom (double crushed)
0.75lbs Crystal 60L (Double Crushed)

Mash temp 154F for 90min (end temp ~150F), Mash Vol ~8gal.

Pulled the grain bag with squeezing and measured 1.050 OG in 7.2 gal

Post Boil ~5.25gal @ 1.064

Max extraction:
2-Row 12 x 38 = 456
Crystal 60L 0.75 x 34 = 25.5 + 456 = 481.5 / 7.2gal = 66.8 ~ 1.067

Pre-boil extraction:
50 points / 67 points = 74.6% yield

Post Boil extraction:
5.25gal x 64 points = 332 / 481 = 69.1% yield

Both the Pre-boil and post-boil Hydrometer readings were taken with the wort around room temp. I only mixed the mash once during the 90min hold to retain heat. I know the sugars don't evaporate, so I'm guessing it was either my temp was higher than I thought when I measure the post-boil (thermometer read around 70 though), or were a lot lower for the pre-boil reading (taken outside in the cold).

I'm not really upset about the efficiency since I was targeting 1.064 for the postboil OG. Is there another reason why these numbers would be off?

The numbers indeed don't match up. My guess would be that your wort wasn't thoroughly mixed when you took the first reading.

Come to think of it I might not have stirred the pot after pulling out the grain bag. The sample for testing was taken from the valve on the bottom of my pot so it is possible that it wasn't mixed properly.