I believe the best work around here is to create a new revision based on the old file versions.
The workflow to do this has intentionally been changed to cater for release bias and is less obvious than it was in the old base Vault - for good reason, it still can be done though.
You will need to get the previous release of the assembly and its parts to the local machine, change the lifecycle state of the files to WIP and check them out without updating, save and check back in as the new revision.
So 3_A will now become "4" and create notes to the effect that the design was reverted.
There is some other discussion threads on this including: http://discussion.autodesk.com/forums/thread.jspa?threadID=731958&tstart=60 which may be of use to you.
Here are some basic steps:
1. Check out assembly and files to be changed (no need to get local)
2. Go to the history tab in Vault explorer
3. Select the older released version and "Get / Checkout"
4. make sure release bias is on and you select download (check-out already done in step 1)
5. Go to Inventor and open the local copy of the files, save the assembly with the correct old versions
6. Check-in old versions as latest and release with new revision.
Your new rev should be the same as the previous.
Please let me know if you have issue with these steps, if I have missed any or if I have misunderstood your intent.
Cheers,
Allan (Autodesk)
Allan
Product Manager
Autodesk, Inc.