I think I would agree with you about the misreading of the years. Some of those early figures for 4 can be very flowery with a strong down line at an angle and only a very very short cross line at the bottom. With weathering, and inexperienced eye, this can end up looking like a figure 1.
Joseph Empson is more of a mystery. I have the Mallardstown book. This includes graveyards of Tullamaine and Newtown – all near Callan. I can find no Empson in here. These graveyards seem Catholic to me. I may be able to check this Joseph Empson reference; it could be a burial entry rather than a headstone. Mary