Could be a few things. 12" at 1375 is less than a minute of angle (about 0.8 MOA or 3 clicks). It could be that your scope adjustments are not consistent across the full range, not likely with a VX-L but worth checking.
It could also have been some wind etc causing the bullet to drop.
Could also be that you need to validate exbal. Use your data from the 1357 shot and see how it changes the comeups for your 487 and 1011. Read somethingby Shawn Carlock that you should validate at the furtherest range possible.
But look on the brightside, any game within 1000 yds is as good as dead