These trains have been running since about 1992, when a good friend of mine (who is also a railfan) was Rail Administrator for the State of Delaware.
The first year the train deadheaded out of PHL, made a stop at the (then new) station at Claymont, and ran via the Shellpot Bridge to the Delmarva Secondary, thence to Harrington. For railroad buffs, the train continued on to the wye for the Indian River power station on Conrail's Indian River Secondary, where it was turned to return to Harrington and pick everybody up. The problem, of course, was that there was no stop in Wilmington. So in 1993 and later years, the train has been run "pull-pull" with an engine on each end. It runs from PHL, makes pickups in Wilmington and at Newark, where it changes ends and heads across the Porter Secondary to the Delmarva Secondary, thence to Harrington.
The extension to Georgetown is just for people who want a longer train ride. In the past, they've run to Indian River (as described), all the way to the end of Conrail ownership at Frankford, DE, and down the "main line" from Harrington to Seaford, DE. I was unsuccessful in getting them to consider running to Pocomoke City, MD. The "main line" is full of slow orders, apparently, and anyway PC is in Maryland, not Delaware.