[BlackFly]

It's unclear that that would save time. If you put in enough hours to the project, you can get classified as one of those later pass proofers. That is extremely taxing work because most of the scannos have already been found by the earlier proofers. You will "complete" multiple pages without ever finding a scanno. The doubt starts to set in if you are on auto-pilot or not.

Meanwhile, in that early stage, because of the stream of errors, it is easy to pay attention and feel like you are doing rewarding work. Moreover, if you are quite quick and diligent, you can basically just read a book as volunteer work.

Also, sometimes the error is in the source material. Different editors have different opinions about what should be done there. Sometimes I had to re-add mistakes that were "fixed" by early proofers trying to correct grammar, if I recall correctly... it was a while back that I volunteered.