We’re jumping through the C’s rather quickly now, so the question of “Will Iowa’s cycle include D as a first letter this time?” will likely be answered sometime early next year if not sooner. The 1997 issuing cycle jumped from CZ to EA very late in alphabetical order in the counties (which didn’t get enough to begin with), and once supplies were exhausted the late E’s came into play.
The 1997 series used CQ’s, CU’s, and CV’s, but I have yet to see the latter in the wild.