INVALID index while concurrent indexing in progress?

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/14/sql-createindex.html
Description:

I think the INVALID index can use further explanation, in particular, from
my experience it seems like when building an index concurrently, the index
gets inserted and labeled invalid while the index is being built, and then
the label gets removed if it finishes successfully or gets left on the index
if there is a failure while building the index. It is my current
understanding, after experimenting, that INVALID means 'incomplete', whether
that's because it's in progress or because it was unable to be completed,
but prior to my experiment my understanding was that INVALID indicated
failure.

This was especially confusing when we were adding an index to a very large
table because we assumed the INVALID index indicated failure when we
couldn't find any other sign of progress or failure.