From Ray Di Ciaccio’s Thesis from 2009 which documents his development of a GIS for ancient sites (he calls his product DAMP):
“One of the first problems I encountered with the survey data is the lack of global geographic coordinates for the sites. Both the AEP and the KSP use different methods for presenting the geographic locations of their sites; the AEP uses a local coordinate system that corresponds with a map included in the publication, and the KTS gives the coordinates as they appear on the British Admiralty Map. Obviously for the purposes of creating a DAMP map that will include the sites from these projects (or some other survey projects), the localized coordinates are of little help; in order to position a location on the map, one needs the geographic latitude and longitude of that location.
"For some reason – perhaps because of the relative novelty of GPS technology or the ease of using local maps to plot the locations of sites – geographic latitude and longitude have not normally been provided for the sites of a Greek survey project. ”
“ Even a more recently published survey, PRAP ... does not provide such information about site location.”
I dropped a couple of Mr. Di Ciaccio's footnotes. The emphases are mine.