So this is how Breakup Notifier does it. It checks to see that the data is there. If at any point in time, the data I'm looking for is unavailable, I mark that field as "stale", don't vouch for the validity of its contents, and remove the ability for the user of the app to view that data.
When it comes back online, I mark it as not stale, and if it differs from the previous (non-stale) version, I send out an email.
Gotcha. I thought you might report updates only. The problem is that people can also remove their status instead of setting it back to "Single". Focusing on value updates only is probably fine and I'm sure nobody is going to freak out if the app misses a breakup :-P In my case, I was trying to create a more comprehensive notification that covered events such as new relationships (i.e. the user does not have a relationship status and one day finally sets it) and I couldn't afford the false positives.
When it comes back online, I mark it as not stale, and if it differs from the previous (non-stale) version, I send out an email.