Perhaps I'm not explaining things correctly. There's a mode in the Harmony software where you can create new commands by pointing the original remote at the bottom of the Harmony remote, and pressing the button on the old remote. Then the Harmony learns the IR sequence and assigns it to the new command. That command in turn can be assigned to buttons or screen functions on the Harmony remote. It's that sequence that I'm trying to use to have it learn a button on my original remote. It's worked for other buttons (that probably have shorter IR sequences), but not for the one button that send a 3-digit channel change command.
Understood. Learning is the wrong way to accomplish your goal. Harmony expects to learn a single signal, not a string of multiple signals. Your 3 digit channel change is 3 distinct commands which Harmony is most likely going to fail at capturing, as it detects the end of the first command and thinks it's done (which it is).
The reason your method worked in other cases is that you got lucky. You were able to put the commands close enough together that Harmony failed to detect the end of each. Yes, with enough trial and error and quick fingers, you may eventually fool it and get it working. And even if you do manage to press the buttons fast enough and close enough together, the receiving device may ignore digits that are too fast and close together, treating them as a duplicate. In any case, that's still the wrong approach.
What I'm trying to tell you is that you can simply build that same sequence in the Harmony software without learning. Go to Buttons - Screen Options (pick activity then Go) - Sequences - Add Sequence, then build a sequence with your 3 channel digits.
Alternatively, build the same sequence in Favorites.
Since I've been doing remote programming for over 20 years, I've done a lot of experimenting. I have indeed managed to get a 32 button sequence in a single Harmony learn. So I know exactly what you're trying to do. But I used special software to send strings of commands shorter and faster than any human ever could. And I only did it because, at the time, Harmony could only do a max of 5 step sequence macros. Now that Harmony can do 20 step sequences, there is no reason to cram strings of multiple commands into a single learn. So the correct, and easy, way will work fine in your case.