Whatever line we draw is going to be kind of arbitrary. The line Mal suggested is not unreasonable.
In fact, it might be easiest on the DMs/judges if we just said "all future xp awards" instead. If we stick with Mal's suggestion, we'll have to remember -- possibly months from now -- when this proposal passed and when various encounters started. Sounds like work.
I'm aware that there's a potential conflict of interest, since both of my active characters have completed encounters but not received xp for them yet. In Ikni's case, several encounters.
I think a bit of extra work is worth it, to avoid the appearance of judges favoring themselves, but necessarily willing to force other people to do extra work so I can avoid showing myself favoritism.
Bottom line, there are arguments either way. Stonegod, what do you think? Incarnation is someone who stands to fall a bit farther behind for having just been granted xp recently, if we allow double xp for previously completed encounters that haven't been awarded yet.