In assembler (not on a '51, but that's unimportant) the equivalent of a switch/case statement with consecutive values went like:

  dec a
  jz  DO_SOMETHING
  dec a
  jz  DO_SOMETHING_ELSE
  dec a
  jz  DO_SOMETHING_ELSE  ;do the same for both cases
  dec a
  jz  DO_SOMETHING_DIFFERENT
  dec a
  jz  DO_SOMETHING_MORE
etc.
 

I needed to insert one value into the list (and shift the rest). As the "insert into list" involved also changing several tables and some other code, I did it conditionally so that I can revert quickly in case of problems. Of course I use copy-paste often.

  dec a
  jz  DO_SOMETHING
  dec a
  jz  DO_SOMETHING_ELSE
  dec a
  jz  DO_SOMETHING_ELSE  ;do the same for both cases
  dec a
.if NEW_STUFF
  dec a
  jz  DO_THE_NEW_STUFF
.endif
  jz  DO_SOMETHING_DIFFERENT
  dec a
  jz  DO_SOMETHING_MORE
 

The error went unnoticed for years, as its symptoms were incidentally masked (by the order of commands arriving from a different device). Now the error somehow surfaced and I had to find it. After a couple of tests i KNEW it is in this sequence, but it took me half a day to spot it.

Of course, most of bugs look trivial *after* you find it.

JW