Brock Through Walls, Pidgey method HP - Page 1
I was doing some experimentation with the any% no save corruption route in Pokemon Blue, and after getting frustrated trying to get a Pidgey to 15 HP, I decided to just wing it and try with 13 HP. It worked! I got all the way to Saffron with no issues.
I don't know what all this means for the HP requirements, but I don't think 15 is as rigid a requirement as it seems.
I did this on the 3DS VC version. I'll give it a shot on BGB tonight with different RAM values to see what happens.
Try reproducing this with another save file. My guess is that the game luckily found some matching data that was not related to your Pidgey, but I can be wrong.
I was able to reproduce it in BGB. My Bulbasaur was level 7, had 14/24 HP, and had 13/12/11/16 stats.
I used the RAM editor to try every value of HP from 0 to 19 on my Pidgey.
If my Pidgey had 6, 8, 10, 13, 15, or 17 HP, I managed to Brock Through Walls all the way to Saffron just fine with no trouble.
If it had 4 or 16 HP, I was able to Brock Through Walls to Saffron, but I couldn't open the menu or talk to anyone once I got to Saffron Center. I could access the PC in the Saffron Center, and from there I could change boxes and reset to get rid of the effect.
If it had 18 or 19 HP, it filled the RAM with garbage and crashed.
If it had any other value, it didn't allow enough freedom of movement to get to Saffron City.
This will need some additional verification, but from the looks of it there are at least 6 values of HP you can use for the Pidgey BTW method, not just one.