Article: Generally, post-punk music is defined as music that emerged from the cultural milieu of punk rock in the late 1970s, although many groups now categorized as post-punk were initially subsumed under the broad umbrella of punk or new wave music, only becoming differentiated as the terms came to signify more narrow styles. Additionally, the accuracy of the term's chronological prefix "post" has been disputed, as various groups commonly labeled post-punk in fact predate the punk rock movement. Reynolds defined the post-punk era as occurring loosely between 1978 and 1984.

Now answer this question: Why has the prefix 'post' caused a bit of dispute as it relates to various post-punk groups?
predate the punk rock movement