After changing the mailbox you dont see any of the Mails which are stored in local Archives by thunderbird

Hello ! Thunderbird is runing on Mint Linux. There is a Email account on Austria A1 (Telekom) This account has primary a number such as aon.999999999@aon.at and you can make an alias on it just as "your_name@aon.at". Tihs account has been reading with thunderbird for 2 Years. now A1 has posted, they have to change the number. So they did but the alias has stayed the same. Before this I have made 3 local Archives with thunderbird named 2024, 2025 und 2026 in which I transfered the elder Emails I wanted to keep. After the Change from A1 the local Archives still can be seen by their names but when you klick on them you dont see any Email. What can I do to get them back ? I had a look at the dataset where the data are stored, and in Editor I still find the Emails, but not in thunderbird. thank you for your advice - and sorry for my poor english. grretings from Austria