As we get questions from data users in different forums than this one (email, phone calls, etc.) I'll try to keep an eye out for those that deserve a broader audience and we'll post them here.
For example, we sometimes get questions about the life-cycle of FEC ID's - most importantly, whether the same candidate or committee could ever have more than one ID.
The generic answer is no -- but there are always exceptions. . . The same person may have more than one candidate ID if they run for different offices - e.g. House members who run for the Senate or congressional candidates who run for President. In these cases the person will have IDs for each office.
Committees will keep the same ID as long as they are active, but if they terminate their activity and stop reporting for a period of time and then register again they would get a new committee ID. This is VERY rare so there shouldn't be more than a handful of examples (I can't think of any off hand).
The more complicated question comes when a candidate decides to run for a different office but uses the same committee they had authorized for a prior campaign. There's no legal problem with this, because candidates are free to transfer left-over funds from one election to another with no limit. The problem comes when they do this in the middle of an election cycle - in these cases we don't have a good way of dividing the committee's financial activity between the two, so we end up including all of the two-year cycle information in the current campaign (luckily, this is probably the most politically reasonable way to treat this too).