The 1878 Morgan Silver Dollar has versions of the back with 8 tail feathers on the eagle, and 7 tail feathers. Plus versions of 7 over 8. There was a concern at the mint that all eagles on coins had odd numbers of tail feathers, so it was changed after the fact. Led to the mix ups.
The road block to a complete collection is 1895, they minted only 880 proof coins, which make the whole collection unattainable for most. Still, most of the dates can be had in a lifetime. History and politics had dramatic effects on the minting and distribution of the coin. It will be an adventure to collect them,
Along with S, P, and D, you get O for New Orleans, and CC for Carson City. The dollar coins are 90% silver and 10% copper. It goes 1878 to 1904, then 1921. The mint did not strike any for 17 years. Lot of history to unfold. Many dollars were melted by the Government, so no one knows the exact total of them left.
The cover cases for the Professional Coin Grading Service have been revamped and have holigrams. Many fake cases out there. PCGS started in 1896. They use a 70 point Sheldon coin grading scale. Hard to find years of Morgan’s are that 1895, 1893-S, 1895-O, 1892-S, 1889-CC, 1884-S, 1879-CC. You have two proof conditions, PL and DMPL which stand for prooflike and deep-mirror prooflike. The grading services will put that on the cases.