I'd say WI is a revision of the DYLW part as it came later.
The Little Pad melody I'd also say - guess - is possibly a revision of a DYLW part and it fits right over the middle 8 of DYLW. Apart from it fitting musically the themes are both Hawaiian.
Yup WI is basically the same melody as the Keeny waka poola part of Worms...just a different tempo and (I think) a different key...try singing the " Keeny waka poola" section to the " Remember the day, day Remember the night, night All day long" section and it actualy works ..