The RIAA (in the U.S.) also charges for auditing.
Hence, the only reason a label gets an audit done is more for "bragging rights". For example, when an artist releases a new album, it's nice to say "from the quadruple platinum selling artist comes their new release". Additionally, to demonstrate that an artist has a hit album, an audit is often done shortly after an album's release (like what was done for HTDAAB - this way, writers will talk about the triple platinum album). Lastly, I'm sure audits are done periodically to update a label's own records.
However, for an older release, there is no immediate need to do an audit, hence why so many things are out of date.