I was just at the LCS and asked if I could purchase a dateless buffalo nickel or two to experiment on. The owner took out a roll of buffalo nickels he was willing to sell for 15 cents each and allowed me to search through them after he noted a 23-S with a visible date he allowed me to have for 15 cents. After some searching, I found a few more dated buffaloes. I found a 13 T1, one 20-D, three 20-S, one 21, one 25, and this coin: Based on the wavy ribbon I thought this was a 20-S and got it for $0.15, but upon taking it home and examining it closely I found that there was enhanced hair detail. It is a 21-S! Rather dingy condition, but 15 cents for a non-acid 21-S is a heck of a steal. A good hole filler for sure. Check your dateless buffaloes a little closer, folks.
Got a "dateless" 1915-S before. I find a lot of older dealers will mark Buffaloes with a hard-to-read date as dateless. Pre-1925 SLQs are also worth taking a look at. I picked up a 24-D with VG-F details for bullion because there was only the top of the 4 showing, but that was all that was needed to verify the date.