For some reason (dimness, I suspect) I can’t map the copious documentation about mod_rewrite onto my trivial problem.
I fat-fingered my archive format when I switched from numbered to dated archives: the URIs all have a _ before the .html. Not content to leave well enough alone, or perhaps that was causing a problem when the archives were written, I changed the config to remove the offending underscore.
In the meantime, Google and sundry other indexers had taken note of the old format, so switching meant breaking some URIs.
It seemed to me that something like this:
RewriteRule ^(.*)_\.html$ $1.html [R]
should work. But no such luck.
Can anyone show me the error of my ways?