Thanks for posting this Truman. It's surprising to me that only the death dates are on the markers, not the birth dates. Why do you think that is?
It's a good question... it looks like the marker for Esma Ledger shows her birth year... 1928. Maybe it simply comes down to personal wish or stipulation. For the others they give their age... so maybe they just expect the visitor to subtract.
As to the question about the ashes being scattered vs. buried... most of my recent ancestors on my Dad's side (my Grandma, Grandpa and Step-Grandma) were all cremated and had their ashes scattered. I don't think there's a marker anywhere for any of them.
But, just as what happened with Jack in BBM, sometimes ashes are divided so you can do more than one thing... i.e. bury half in Childress with a stone and send the other half up to Lightning Flat in the hopes they'll be scattered.