I don't know what post flashing would do...I do know that pre flashing does wonders to support low values. I would certainly try a post flash exposure to non image bearing light at a Zone III or IV exposure. You have absolutely nothing to lose in trying this.
If there were adequate notes taken for the scene, a decent guess would be to add light in the form of a gray card exposure. As Francesco has mentioned, the scene brightness range is critical. Can you take a test shot with a step wedge, first, to see what the actual values are for an accurate shutter estimate of underexposure?
With good notes taken of the scene, a known value of underexposure from the shutter and a bit of thought, this may not be too bad. If you can get a reading for the shutter from a step wedge (use the same f stop as the original shot to cut down on variables) you will know exactly how much your underexposure is.
From this test and your notes, you should be able to get an idea of a flash exposure to boost the shadows sufficiently. At that point, it is only a matter of development time for nailing down the top for zone VIII. Please let us know how you fare with the process. Chin up buddy, we've all done things like this. The trick is learning from them. Best wishes for a successful development. tim
Thank you all for the information. As always so many around here willing to help. It is very much appreciated. ;)
I developed 2 more 8x10's tonight. Kodak TMAX400 in Pyrocat HD 1:1:100 in JOBO expert drum (I should have mentioned this in my original post)
Looking at these negatives (and the ones from the other night) they look "thin", but there is detail in the shadow areas. Not as much as I would like, but there is some.
I'm thinking that I should be able to get some good prints from them. They are probably to thin for AZO, but as long as I can get a good print I'll be happy.
Jim, since they are on the thin side, give azo a try anyway. I've had this one to deal with and my technique for a thin negative is to give more exposure and then cut development time. I treat azo like a slow film. To reduce contrast you can try adding exposure and reduce development. The increased exposure treats the high values with enough light to make it through the film and get substance in zone VIII (remember, it is all backwards with paper). The reduced development time stops shadows from blocking up completely and turning to tar.
It has been pointed out to me that this is not the correct way to deal with film. It should be the correct exposure and always match the paper's scale. Since I have made mistakes from time to time in my photography, am not perfect and have no real hope of being perfect on each shot, I've had to adapt to my own flaws (rationalization, justification or reality). I hope this isn't too discouraging, but it helps to realize that, try as we might, it isn't always as we wish. So what? As long as we keep plugging away, we will always learn and improve.