How to deal with bug fixes introduced almost at the end of software verification?

A little context: - I'm testing the firmware of an embedded system. It involves calling certain firmware features and checking input/outputs provided by the hardware peripherals.

1. I began testing version A and executed 85 % of my test cases.

   • Then, I found out the developer released version B, version C and version D. Each with small changes.
   • I thought changes in B and C did not affect me.
   • Only re-tested one test case in version D.

2. I found several bugs in version A and the developer now fixed them and he released version E.

3. So, I tested about 90% of the test cases in version A, 4% on version D and 6% on version E.

4. The question I have is, what firmware version can I release? version A because that is the biggest chunk that I tested? or can I say the last one released version E?

5. I semi-automated the firmware interaction of the test cases, but, I have to manually measure the electrical signals. Bottom line is, it takes time to run these test cases.

6. Availability of an appropriate embedded system in which to run the tests is another problem. There aren't many and many people share them.

7. Should I bite the bullet and somehow run all the test cases again for version E?

Thanks a lot,