When my oldest account turned 3 years I saw a similar drop and was told it was due to re-bucketing. I'm curious to see what the effect will be when it turns 4 years next month....
That would suggest though that the presence of a mortgage is a factor in scorecard assignment, which it is not.
While I'm definitely in agreement on checking the reports, being rebucketed isn't outside of the realm of possibility.
I think we're all pretty sold on the fact that age of oldest is a scorecard segmentation metric, and somewhere in there you transition out of the new / thin file score card to the mature credit report scorecards, I just would've figured it would've been prior to that.
That might explain the somewhat freakishly high 1-2 year timelines on FICO 8 for new files, it'd be an interesting experiment to run if I had a new file to play with for perhaps longer than the "how long to 800 does it really take?" that I was originally amused by. Not sure I have that kind of patience really haha, but the fact that it happened to both you and your wife and presumably the mortgage is the only shared account (?) from your description, it certainly points to your shifting scorecards.
Do you get real reason codes from CCT or your other services? That'd be worth a look but FICO 8 reason codes suck across the industry in terms of how many you get so you might not get much.