Google Docs, Sheets and Slides
Within Google Docs, Sheets and Slides, it's easy to copy a voice note from one document to another.
For example, let's say you give an outstanding summary of the events leading up to the American Revolutionary War in 59.5 seconds, and you doubt you'll ever achieve the same heights of succinct story telling.
Step 1 - locate your original voice note, and click the three dots in the top right corner:
Step 2 - select 'Edit'
Step 3 - highlight the comment text, and copy the whole thing.
Step 4 - simply paste the text into the new comment that you wish to leave, and your original voice note will be replicated in its full glory!
You should be able to perform the same basic approach within Google Classroom, with the caveat that the '3 dots' are located all the way over to the right of the comment area in the 'stream' view.
And in the private comments document view, don't forget that there's a 'comment bank feature', where you can stash your voice note links. They don't render as playable cards, but you can keep track of them by editing the language a little, for example: