This year, the PHL-ATH was loaded in the schedule starting in April but they changed the start date to May. It was never loaded again for April but kept it's May starting date. Many of the seasonal routes I look at start May 4th-5th in 2017, ex PHL-ATH May 4th, CLT-MAD May 4th, CLT-BCN May 4th.

I would guess that PHL-VCE would fall into that date pattern.