TL/DR: If you can't get the catalyst monitor to set and have a speed signal converting device on your vehicle, bypass it temporarily to get the catalyst monitor to set and pass the smog test.
So I've seen other mentions here as well as other places from folks having a hard time getting the emissions control self-test catalyst monitor to set.
I've generally managed to make it happen, but it always took a couple of attempts with a very concerted effort to run though five different speeds and holding them. I'd generally get honked at at least once while going through this every two years, and it never set without a concerted effort.
I have relatively low mileage oxygen sensors and a scan tool shows the upstream sensors switching and the downstream one in perfectly flat line, so my converter is working.
Like may of other e-series folks I have a Dakota Digital unit that converts the speed pulses to compensate for larger tires.
This past year I had no luck at all getting it to set, and again the converter appears to be working fine once warm.
So just to try something, I bypassed the Dakota Digital, and the monitor immediately set.
Since my '99 is still subject to an actual test, the test data also shows that the actual catalytic converter is working perfectly well.
After getting my smog cert, I disconnected the battery a couple of times and the monitor sets reliably after just about any short drive.
So, for my case at least, that's one more mystery solved.
(Yes, I've not been hanging out here much, but wanted to record this bit of information somewhere public in the hope that it helps someone, it would certainly have saved me some frustration.)
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