Hi Sarah,
Just a quick addition to Shal's remarks.? My group's transferred messages contains a special header field called "X-Yahoo-Msgnum" that should correspond to the original Yahoo message id. Hopefully we can figure out how to use that to help match files to links to the transferred messages. We would need to figure out how to create an automated script to do it, but hopefully that's doable.
It's also possible to download the archives of a Groups.io group. That also might help automate the process. The trick will be to be sure that we can correctly match the Yahoo ID to the Groups.io message number that is used to reference the message.
We may need some help from the Groups.io support people. I'm hoping that we can convince them to do a trial transfer of your group so we can work things out in advance.
You won't need to post your file here, since I am also a member of your group. The file in question contains links corresponding to Yahoo message numbers. The only technical problem is the matching that I discussed above.
David.
David Andrews