You might have seen the National Do-Not-Call Registry popping back up in the press recently — since the Federal Trade Commission opened the list in 2003, and numbers registered on the list expire after five years, there are a ton of numbers that’ll fall off the list next year unless people go and re-register them.

I discovered one annoying gotcha, though, related to how the FTC set up the online system for registering numbers and reporting violations of the list. Consider the following three bits of info:

• the online system doesn’t make any distinction between registering a number on the list and re-registering a number that’s already on the list;
• the law gives telemarketers a 31-day window to continue to call people after listing their numbers;
• the online system doesn’t let you report a company’s violation of the registry if you’re within the 31-day window.

What that means is that even if you’ve had your number on the list for years, if you re-register it, you’ll start a 31-day clock where you can’t report any violations. It’s pretty annoying, actually — but of course, it’s certainly not a reason you should avoid making sure your numbers don’t fall off the do-not-call list.