grent - where did you find this?? There used to be a regulation, 38 CFR 4.16c, that stated basically this but it was rescinded 10/8/96. As others have stated, you should apply for an increase to 100% or TDIU. In that TDIU request I would add the following statement: If for any reason I am found not qualified for TDIU, based on 38 CFR 4.16a, then I request "extra-schedular" consideration, under 38 CFR 4.16b, as I am unable to work due to my service-connected PTSD.
pr