I made a V.A. disability claim back in december of 2006. Backpay?

It has been repeatedly denied because the V.A. lost the portion of my medical records that confirm incident happened during service. Over the years i have sent them names dates places and all info they needed to find copies of records. Still repeatedly denied due to NO EVIDENCE. I havent had the amount of time needed to work on case as much as i have had recently because i was working as a security contractor in Kuwait. Since getting home back in October of 2010 i resubmitted and personally tracked down all supporting records to include co-worker and family letters and official government documents to prove it occured during my service. All the info i obtained was in the places i had told the V.A. for years, why they didnt obtain the records themselves i do not know. I have been told by my V.A. regional rep that it is plenty of proof to get claim approved. I also consulted with, but did not hire private attorneys, who said i should be paid all the way back to 1998 when the incident occured in service because the Marine Corps did not follow the appropriate laws, policies and MCO's that dealt with my problem. I was actually NJP'd, rank taken and never given medical treatment after initial treatment even though i asked repeatedly for it. Also i was treated at Camp Lejeune Hospital for the injury but they also can not find an inpatient record, neither can V.A. neither can the National Personel Records Center. Its like the military medical records pertaining to this just disappeared. I do have evidence from Police Department Report and ambulance service from out in town taking me to Camp Lejeune. After that its like the records fell off the face of the earth..... My question is will i get backpay to 1998 (in service) or Dec. 2006 (first claim) or Oct 2010 (last claim)? My V.A. regional rep said im looking at 70% or more from his experience.