[pinkpanther]

But if it wasn't written by the original author, would you say it is a forgery?

Take the longer ending of Mark as another example. Scholars say it wasn't written by the original author of Mark, which means someone else added their own words into that book. Would you call that a corruption?

Nope ..it is not a corruption..no scholars will say that
this does not automatically imply that the entire Gospel is corrupt. It simply highlights the dynamic nature of textual transmission and the scholarly process of identifying and understanding variations in ancient texts.