"Skype stores the chat history of your account locally or hard drive of the device being used.
If you no longer able to view the message from your end, it will no longer appear.
Please make sure that from your settings, your messages is set to be saved forever.
The only conversation that we can guarantee you reflect is the last 30 days of your conversation history as this is stored in the cloud, so you can access it when you're signed in to Skype on any device.
Thanks,
Rommell_C
Skype Community Moderator"
https://answers.microsoft.com/......5a036c77de