Happy New year everybody!

I wanted to test if I could develop infinite lives Cheat for SMB1. So I dissassembled SMB1 rom with TRaCER. Then I studied the code for few hours(I'm a newbie). I thought the amount of lives was substracted with SBC.So I listed every SBC $01 and SBC #$01 and one at a time replaced them as SBC $00 or #$00.

That resulted few Graphic bugs, but the amount 0f lives was still dropping at every death...

Then I tested GG code that gives infinite lives(SXIOPO), that worked fine.
Nesticle said the code patches address 91D9 with AD.

In both of my dissassemblations(groovy word)(without ines header and with)address 91D9 was information or "???".

Where do this patch really belong to?
I don't really care about the code, but I want to know how is it done.

I'd really appereciate if somebody could help me with this topic.

And btw I found this thing on SMB's code:

00/8057: 4C 57 80 JMP $8057

What's the purpose of this one?
Is it waiting for some interrupt or something?