I had a 3 reservation in my own account just as a backup if I ended up not buying the X. My wife had a day one reservation in a separate account. I decided it would be easier to share the cars if we used the same account, so I bought the X in my wife's account. I expect she'll get the 3, the X gives her better priority, and it should be easy to switch between cars. I expect to cancel my reservation eventually unless someone in the family wants it.
All of that works up to this: Yesterday I noticed my 3 reservation had been moved to the account with the X and the wife's 3 reservation. We did have the same contact info, though different email addresses. Now it shows the X and two 3 reservations. My old account seems to have been eliminated. Kind of strange, but maybe they're cleaning up their reservation accounts, or looking for anyone who reserved more than two.