Good news! The folks have found the issue here - there are a handful Ideas that didn't migrate correctly when Labs first launched, and this is one of them. They're going to dig them out and get them moved over properly, which should be before the end of January. They'll keep their status, so any of them that are marked as Implemented will automatically assign the sticker to the member who posted them within a day or so of the migration.
@tradertall - Labs Payback queries are best directed to @prescilla_g, but from what I remember, Payback on Ideas isn't based solely on interactions - it depends on the idea's progress, so isn't necessarily tied to the date the idea was posted or the vote was made. One constant is that we'll never retroactively add Payback to a period that's passed, though - it'll always be folded into the current month's Payback even if it's activity that took place on something that was posted months before.
giffgaff community staffer - let me know if you want to chat about anything. You can send me a message and we'll get rolling. Need a topic? Try here.