Does this happen less frequently than in the past?  If so, I’m sure it’s not because we got better at avoiding mistakes.

If a book has an error on a single page, you can reprint that leaf and replace the offending page.  The old page is “ripped” out — actually carefully cut out using an Xacto-type knife, a metal rule, and a backer board which is slid between the leaf in question and the next. The reprinted leaf is cut to size, pasted down the inner edge, and tipped onto the stub left in the gutter where the old pages were removed.

This sort of work is now done at specialist book repair plants, but in the olden day used to be done in every bindery.  Now that the craft of book binding, like so much else in the book manufacturing business, has largely been engineered into the machinery, the many craft and hand workers in the bindery have disappeared.

Two factors may lead to our ripping and tipping less often — shorter print runs, meaning there are just fewer copies needing to be corrected when the error is discovered, and the  reduction in the “value” of the physical object which is the book, as against the cost of labor. Perhaps we tend nowadays to insert an erratum slip, and then incorporate the change in the next reprint.