You can see a copy of the deed at the Berks County Recorder of Deeds site, start here. https://counties2.recordfusion.com/countyweb/login.do?county...
You have to sign up but it is well worth it. I followed the 1810 deed up to the present land owners, looking for any hint of the burial ground or mention of the original land grant, didn't find anything. If you have any questions on the deed or deed site just ask me at firstname.lastname@example.org
Who were the folks who set up the dedication of the new headstone? Were they perhaps the Schmehl Family Association? That at least shows that someone was around as late as 1994 caring about the graveyard.