Hi @Martyn_Foster! Welcome to the Community forum 
Thanks for your patience as I have been testing things out and hopefully offer a bit of guidance here!
For the review form, have you tried setting the form's key property to {{ urlparams.draft_id }}? This should fully unmount/remount the component whenever the key changes. To test, you can type a comment, switch drafts, switch back - and the comment should be gone, not carried between switches. This should help with the stale unsaved comments applying to the wrong draft.
Not sure how you have your tables set up, but you can insert into reviews and update the status and version in drafts at the same time.
Other suggestions:
Upon saving, you can create toasts for On success (to indicate that the review was saved for [draft name]) and On failure (to tell the user to reload to latest version) so your reviewers can have clear info on what is saved/not saved.
I'll continue testing around to see if I can answer your other questions!
Lastly, just wanted to mention that we have live Office Hours on Tues/Thurs where we can take a look at your app and troubleshoot together! It may be easier than writing back and forth 
-Jen