Comment 0 for bug 1183759

Suppose we get error reports from a machine running Ubuntu version N.

Later, we get error reports from the same machine running Ubuntu version N+1, N+2, or whatever.

Provided that we don't get further reports from it running Ubuntu version N (indicating a dual boot), it's safe to assume that it doesn't have N installed any more.

However, we don't remove it from the count of machines running N until 90 days has passed without a report.

Hypothesis: If we fix this, the October-to-January dip in <https://errors.ubuntu.com/?release=Ubuntu%2012.04&period=day> will disappear, because it was caused by 12.04 users upgrading to 12.10.

Similarly, the post-April plummet in <https://errors.ubuntu.com/?release=Ubuntu%2012.10&period=day> will disappear, because it was caused by 12.10 users upgrading to 13.04.