“You can reclaim groups with old e-mail addresses using the memwiz (https://joshuatj.com/2018/07/18/your-email-address-is-not-linked-to-a-yahoo-id-yahoo-groups/). It works even if your e-mail just happens to be same as a long deleted one. I’ve recreated some hotmail e-mails that don’t exist anymore ….and tried the memwiz on them. Most had no groups attached but two have and I was given access to them.”

See:  Your email address is not linked to a Yahoo ID — Yahoo! Groups

https://joshuatj.com/2018/07/18/your-email-address-is-not-linked-to-a-yahoo-id-yahoo-groups/