I've not seen an answer for this mass 301 redirect issue specifically
Well, no, you're not going to find a thread that says how to redirect the exact URL 123-rest-of-name to the exact URL rest-of-name
But there are hundreds of posts detailing RewriteRules that will do the trick.
If you already use mod_rewrite (RewriteRule by that name, regardless of what it does) then any redirects in the same htaccess also need to use mod_rewrite.
If not, you can use mod_alias in the RedirectMatch form. You need RedirectMatch (or RewriteRule) rather than simply Redirect because you'll be setting up a simple Regular Expression and capturing part of the request.
Based on your examples, it looks as if both types of redirect can be collapsed into a single rule.