Plan

Premium

Country

 Germany

Device

iPhone 8 Plus

Operating System

iOS 11

My Question or Issue

Please explain how downloads are expiring or however it works, because I have quite a few offline songs/albums/playlists. Some of which change (and of course new songs need to be downloaded) - but others are perfectly static contents but will be re-downloaded every-so-often anyways. 

This is a pain-in-the-a** as I work on a ship and WiFi is really really bad and options to get a better connection shoreside are very rare. 

I understand new songs need to download of course - but what can I do so that unchanged contents do not re-download??

thanks