Noteoff Nightmare! How to shift a midi note's pitch without confusing the velocity?

Hello! I'm new here, and new to max. Some experience with pure data, but MAN I'm having trouble with this midi routing stuff.

I'm working on a patch that periodically shifts incoming midi notes. Think, "down an octave every 13 notes" or "up a fifth every 7 notes" - and it's working! I'll attach a link to a sequence/melody made from just one 5-step sequence run through two instances of the device. I'm calling it "yarn adder" because it reminds me of the patterns that show up when knitting with multicolored yarns.

But... when I said it worked, I wasn't exactly telling the whole truth. If you send more than one note at a time, there's a chance that the adder will shift a note's pitch TO the same pitch as another note. If this happens, the noteoff (0 in velocity) doesn't know which one to turn off, and will occasionally leave one of the notes playing. My workaround is to never send more than one note through, but there's clearly something wrong with the stripnote/unpack system I have set up right now... And that bugs me!

Please take a look, I'm sure it's an easy fix, I'm just new to midiin!

Thanks,
Nico