in my experience as 75k, when i change an award, i am guessing the date is reset (my mileage activity is +x miles and than -x miles (indicating that it was redeposited and then booked as new) but again, it could be because i am 75k.

(I changed the award because i paid 12.5 already so i book something far out as a place holder so that I can change that booking again to avoid the 12.5 fee).