you're absolutely right. However it seems to be correct to send PC#124, even though the controller actually outputs PC#123, since it brings up the "TUNER" label in the H9.
If I try instead sending PC#125 alone (PC#124 in H9) it just toggles the H9 state from active/bypassed, which is correct according to the default H9 midi map. No tuner.
However I observed that repeatedly sending just PC#124 (H9's 123) causes the H9 to cycle through these four states:
1- just TUNER label displayed but no guitar audio
2- back to effect sound
3 – perfectly working tuner
4- back to effect sound
We just looked at the tuner setting in the H9 pgm change map, and you're right. There is a bug in the latest H9 software release. The tuner is assigned to MIDI program change 123 (or 124 if you start counting with 1), but it doesn't appear in the program change map. The assignment above that (124) says "TOG" and toggles between active and bypass, and in the past I had seen that text and thought it meant toggle tuner on and off and overlooked the error. But actually the tuner just isn't appearing in the list, and there's no option to select the tuner.
We've fixed this in the version of H9 Control we're working on. That release isn't out yet, but when it comes out, you'll be able to adjust the tuner assignment there. The new release is going to be v2.5.0. Hopefully, it will be posted for Mac and Windows tomorrow and for iOS at the start of next week.