search is ignoring old PBIs

[Joe Harris]

I'm trying to search for a particular PBI using the "Search JIRA" box in the upper-right.  But search is ignoring any PBIs made before a certain date.  (I don't know what that date is.)   

If I slog through the backlog, locate that PBI, make a tiny edit and re-save, then that PBI will show up in searches.  So, it's not like I don't have permission to view that PBI.  It's just that the search was ignoring that PBI, because it was old.

What's going on?  I swear this problem wasn't happening two weeks ago.  Why is JIRA ignoring old PBIs?