Studio overdubbing is a very common practice for doctoring live performances. It's used extensively in rock oriented performances to fix performers' mistake(s), to obtain a better recording of a specific instrument (typcially a vocal), or to add an instrument missing from the original live performance. When skillfully done, as in "Waiting For Columbus", it's essentially unhearable and is a positive addition to the final recording. Any multi-track recording, one where individual instruments are independently miked and assigned to a single recording channel, is fair game for this type of studio manipulation.