Schedule changes occur somewhat more frequently that I would have expected. Had this happen many times...purchase a ticket a few months in advance...schedule changes so connection is no longer legal...flight gets changed.

CO Insider, perhaps you can take a look at the notifications of these changes. For some reason, the notification system appears to be quite sporadic. I've seen many similar posts where the OP doesn't get notified of the schedule change in advance...happened to me a couple times as well...only way I found out was by logging into CO.COM and looking at the itinerary.