I have been editor-in-chief of two professional journals over the time period 1976- 2001. "In press" to me meant that the articles I had selected for publication were then being worked on by the publisher---letterpress or photo-offset---and would be released to me for final proofing on letterpress journal copy or a final OK to run on photo-offset. With my OK, the journal would be mass-produced on a time available basis and mailed to subscribers by the publisher to meet the monthly or quarterly deadlines I had imposed on them and that they understood.
The authors were not given an opportunity to revise their manuscripts once the "in press" designation was in place.