Miles are posted to the AAdvantage account once a month. If your April charges appear on a May credit card statement I would expect them to count, but I have not followed this issue closely.
I'm going to go with the safe route. Basically I won't pay for any large expenses like taxes until May 1st at the earliest. I'll probably test out my theory with something cheap like a dollar or two from April 26th or so and see where that will lead.