There is nowhere to send it yet
This site has no address taking reports at the moment, so the box that would carry one is not on this page. What a report needs does not change: the pattern, the piece, the round number, the count the page gives and the count you got.
Note them against the round while you have it in front of you — a count reconstructed afterwards is weaker evidence than one taken at the row. They are worth keeping whether or not anything is open to receive them.
What happens to it
The round goes back through the same validator the pattern passed, with your count beside it. If the chain is wrong the pattern is corrected, the checks are re-run, and the date those checks carry on its page moves.
A fault in one pattern may be a fault in whatever drafted it, in which case it is sitting in others too. That is why a report naming a round is worth more than the round: it is what turns one broken piece into a rule that can be run over all of them.
When there is somewhere to send one, what comes in gets published — the report, the round it names, and what came of it.There is no error rate on this page until there is one to count.
Not a count?
A report is worth writing for anything else that is wrong on a page: a finished size that cannot be right, a name that promises a texture single crochet cannot make, a piece that closes on a hole nothing shuts.
The pictures are worth naming on their own. They are rendered from the stitch counts, never photographed, and nothing has yet compared one against the pattern it came from — so a render showing a piece the rounds do not make is a fault worth reporting and one the checks cannot see.