>It will output stuff from open source projects verbatim

I've seen this too, however only in pretty artificial circumstances. Usually in empty projects, and with some combination of exact function names/signatures, detailed comments, or trivially easy blocks that will almost never be unique. I've never seen an example posted in-context (in an existing project with it's own conventions) where this occurred.

>One solution without messing with co-pilot training or output is to have a second program look at code being generated to see if it's coming from any of the open source projects on gitbub and let the user know so they can abide by the license.

This kinda exists, there is a setting to block matching open-source code although reportedly it isn't especially effective (then again, I've only seen this talked about by people who also report frequent copy-paste behaviour, something I've not been able to replicate in normal use).