Thanks! I exported my data through this and it didn't take too long. Unfortunately this has the same issue as every other data export tool, in that it doesn't let you infer context in surrounding messages, it only saves yours.

Also apparently chat logs didn't start being kept until sometime around 2017, most of my extensive skype use was around 2014, so I reckon it's all gone by now. Shame.

Skype chats used to be peer-to-peer, so older history would only be kept locally by the client. If you have backups of your user/home directory from that time, it might be recoverable. IIRC they were stored in an SQLite database, so it's not too difficult to export them.