Q: using iTunes version 12.2.1.16 on a MacBook Pro what is the best way to re-download previous purchases that no longer show up in my library?

You need to make sure that you are signing in the same Apple ID as before, from the same country as before.

You can read this Hide and unhide purchases in the iTunes Store - Apple Support to make sure your purchases are not hidden.

Then, follow See your purchase history in the iTunes Store - Apple Support.

If this doesn't work, call Apple Support.

If the rights-holders have removed the items from the store, or if you've moved countries since buying them, you won't be able to redownload them.

Audiobooks and tones are one-time only downloads, they won't show for redownloading.