We don't use RE to claim GA, but do import gift data from the system that we do use. Some of these gifts can be much earlier than the current GA retrospective limit, but RE won't let us flag them as having been claimed on, even though the claim was perfectly legitimate at the time. We may be a bit unusual in our set up, but I suspect this may affect other on occasion, e.g. if merging old data/dbs that all contain GA info.