RickyC, Thank you for your service! I know you're asking someone else, but I'll provide my info too (always good to have extra perspectives 
I just finished going through TDPD forgiveness process. I have a Total Permanent Disability rating. I emailed to the nelnet email address my Benefits Summary Letter, Benefit Verification Letter and the TPD application. I recieved responses via email and mail that they received the application and were processing it. A few days after emailing Nelnet, my student loan went into forbearance. The process took 55 days until it was approved (I checked on their website for status update and shortly thereafter received an email and later a letter). About 6 days after approval, I had a zero balance with my student loan lender (still waiting for them to report the new balance to the credit bureaus). Two weeks after the loan discharge approval, I received funds towards payments I had made to the lender since my P&T effective date. One thing I didn't do, the Benefit Summary effective date was December 1, 2017 which wasn't the effective date of my P&T, it's the effective date of the last COLA change for disability pay. A letter from Nelnet informed me if the effective date was different than Dec 2017, to send them proof. I emailed them the first part of my last decision letter from the VA which showed the earlier effective date. About a week later Nelnet approved and notified my lender. Hope this helps and please feel free to reach out if you have any questions.
Hi RickyC - Unfortunately I don't really know how that is determined or how to go about making it that way. I've read in a forum that age and type(s) of disability and how they affect the quality of life and ability to find employment may be a factor for determination. I got a lot of info from a forum called Veterans Benefits Network or VBN. I've read some folks were granted discharge without P&T by just submitting their Benefit Verification Letter which is downloadable on eBenefits. That letter doesn't say whether it's P&T or not, just the date of letter, effective date of disability, and 100%. Whether true or not I can't say for sure. I submitted both thr verification and summary letter because the summary letter does state P&T and I didn't want any decision delays My P&T came after an appeal process and I was quite surprised. Hope this helps, be gld to answer and other questiosn. Best of luck!
Just an update, all the credit bureaus show a zero balance on my student loans! However, this has had no affect on my FICO scores 
FICO 8 scores remained the same. I was hoping for a boost with my FICO mortgage (2,4,5) but nothing there either. Or well, I'm certainly not complaining, we will call it an observation