And here is a grommet comparison. The one on the left has been filed and the one on the right has not.
While filing a half moon sliver of metal came off, which was very satisfying. To test smoothness I pushed a cotton swab through the hole to see if it's would catch. Nope. All smooth. Filing has saved this pair of stays. Before starting this corset documentation project, this is the exact sort of problem that would have landed this corset in the bin of unfinished projects. Thanks for all the suggestions, they spurred me to action.