Obviously it can be four or five - I'd have thought that was a given, bearing in mind that attacks of more than five or less than four bowlers is almost unheard-of. But yeah, what did you think I meant by "one of the finest attacks Test cricket has seen" if not one of the best ~20 attacks in history?
As I say, precious few attacks play together for more than a series or two. Even the two who I'd tend to rate the best two ever (Roberts, Holding, Garner, Marshall and McGrath, Gillespie, Kasprowicz, Warne) played for no more than a few months. About the only truly superlative attacks I can think of which played together for more than a few months were the West Indians of 1979/80-1981 (Roberts, Holding, Garner, Croft) and Australians of the late-1940s (Lindwall, Miller, Johnston, Toshack) - even they hardly stuck around for all that long.