Yes you cannot get both VA and military pay on the same day. One drill = 1 day, so two drills in one day = two days of concurrent pay.

So a theoretical reservist doing 48 drills + 12 days AT would have 60 days of concurrent receipt.

You have the choice of either waiving VA pay or waiving drill pay...I think it always works out much better for you to waive 60 days (2 months) of VA pay rather than all of your military pay. You'd probably have to be pushing 100% for the VA pay to be worth more than mil pay.

Best to be pro-active on this, and pay up every year rather than wait for them to notice and send you a bill. They should send you a letter each year.

In my case, I just allow them to offset my VA pay, so I don't get VA for 2-3 months depending on how much mil I did last year.