Different Grades Of Diffrent Denominations Of Coins...

I was trying to grade the half, and used the dollar as reference, but realized quite fast that I wouldn't be able to

It will be quite expensive to have a reference library of all denominations, but a fun task :P

I am not sure there are any different grading standards in a specific TPG throughout all the different series of coins (even though there will be discrepancies because they are human) but there are different grading standards by different specialists of different series like EAC for copper and bust half collectors and so on. The census is that your Barber was AU-MS-64 and you are looking at a 65 Morgan, there wouldn't be very much difference between a 64 and 65 coin. It could be one hit in a focal area of the coin to more hits on the Reverse or anything like that. A coin can also look like a MS-64 as far as hits goes and still be an AU coin because there is wear on the high points. It can be almost virtually hit free and still be an AU coin because of wear, that is why ASU-58 is such a sought after grade. In AU-58 you have the details sometimes of a MS-64 coin with just the slightest bit of rub that breaks a little of the luster in a spot or two. I hope this makes sense to you and if not just let me know and I will try to explain it better. I guess an easier way to say it is in AU and below it is wear that determines the grade in MS and above it is hits that makes the coin a specific grade.