Hi babblon,
Thanks for contacting Apple Support Communities!
We understand that when you sync new content to your iPod, the previous content is no longer available on your iPod, correct?
Do you use Sync Library? This article explains what Sync Library is and what it does: If songs are missing from your music library after you turn on Sync Library - Apple Support
You can also reference this link which explains how to sync content with your iPod via your computer: Sync iPod touch with your computer - Apple Support
"Sync iPod touch with your computer
You can use iCloud to automatically keep your photos, files, calendar, and more updated across all your devices where you’re signed in with your Apple ID. (You can even use a Windows PC to access your iCloud data on iCloud.com.) Other services like Apple Music allow you to access additional content across all of your devices. With iCloud and services like Apple Music, no syncing is required.
If you don’t want to use iCloud or other services, you can connect iPod touch to your Mac or Windows PC to sync the following items:
- Albums, songs, playlists, movies, TV shows, podcasts, books, and audiobooks
- Photos and videos
- Contacts and calendars
With syncing, you can keep these items up to date between your computer and your iPod touch.
Note: If you use iCloud or other services like Apple Music, options for syncing with your computer might not be available."
We hope this helps.
Cheers!