Sorry, I cheated a bit on this one. PCI graded it. At first I thought they got it right, but the more I look at it, I don't think it has the luster for a 65. I would call it 64. As noted, the coin is nearly nick free. The strike is very good particularly for a branch mint. Abe even has a very nice beard. The wheats may not be sharp, but every one of them are there. FWIW, 3 of the 4 certified Lincolns from this date have very similar looking wheats.
You know these and luster better than I do but I think it has a shot at 65 with NGC. Probably not at PCGS. I'm not very good at understanding luster on brown copper from images. Nice coin.
Although it would be a bad decision to try for a NGC Grade, it would be interesting to see their Grade. Already having a MS65 would be too risky with little or no value added, I think you got the best it could be, Congratulations.
The reality of grading IMO has a lot to do with the market. Any close grade like F15 to VF20 is so close it would become the graders attitude at that time. As I am sure you are aware timing of the markets can play well with Market, Technical and TPG Grading Standards. I have a tremendous respect for PCGS and NGC they both are just humans calling em like they see em at the time. As a vendor or collector you accomplished well with the MS65 Grade on a purchase of a MS63B Coin. Vendors hope for those purchases sometimes were right and sometimes were wrong. We are just playing markets in our own way. Hopefully as Dealers we are right more than wrong. If it was me purchasing that 1916 D Raw I would not want to risk more than 63b pricing.
If it were my coin, I would either keep it as is, because I don't really care about the grade on the slab as much as the coin inside. Either that or I'd get it out of that gold label slab immediately because I've seen some evidence those aren't inert like other slabs out there. But, I don't think a crackout attempt would be unwarranted. If it could get into an MS64 holder from PCGS or NGC, it would make the coin a lot easier to sell, and would break roughly even in value after grading fees. If it could make it into a PCGS/NGC 65 slab, then we're talking a decent bump in market value, but leaving it in that PCI slab doesn't seem worthwhile if you want to sell and can only get 63 money out of it.