What I do if I use a function or a routine obtained from here or anywhere else it to put a comment before the routine in my source code - at least I remember then. Somthing like:
;----- LASER EYE ROUTINE BY Billy the Blitz Bomber-----
;----- amended 10/04/2004
Function LASER_EYE()
etc
;----- LASER EYE ROUTINE BY Billy the Blitz Bomber-----
;----- amended 10/04/2004
Function LASER_EYE()
etc