How many times have you said: "Oh yeah, I forgot about that requirement…" or "I think we talked about that a couple of weeks ago, but nobody added it to the project tracker?"
Here are some indicators that there is work that you need to do that is not captured in your current project management system. They should work well with almost any agile project management system. It's a good way of finding and capturing latent stories for people on the project to see.
Patterns to watch for
"We need to revisit this in October." or "We should probably do this at some point."
Create a story for this item. Regardless of when you revisit the item, it's nice to visualize the work that you believe you should do at some point. This can be effectively prioritized against the other work. You capture that you have something to do and can plan around it. This is useful in capturing work expansion as it happens.