I made an attempt at this a while back, first disassembling by hand, then with the aid of a homegrown disassembler.

Unless your disassembler is extremely intelligent, it's most likely screwed up the jumptables. SMB (and a number of other nintendo titles) do something like this for jumptables:

LDA #$03
JSR do_jumptable
DW $A020, $8002, etc

do_jumptable:
ASL A ; adjust index into table
TAY
PLA ; grab high byte
STA $01
PLA ; grab low byte
STA $00
INY ; point at the low byte of the entry
LDA ($00), Y
STA $03
INY
LDA ($00), Y
STA $02
JMP ($0002)

Their version is probably a little bit shorter, as that was from memory. That pops the return address off the stack, and uses it as the base address for a jumptable indexed by A. The RTS at the end of whatever bit of code that entry points at will return to the first function's caller.

Nintendo likes to nest these, I think I remember seeing a set that was 4 tables deep in SMB1 somewhere.