Taken together, these two data sets tell me that pecan trees may have a way of regulating crop load that has nothing to do with pollination. If a tree produces an excess of pistillate flowers ("on" years) post-pollination nut drop will appear severe. In contrast, trees during "off" years seem to want to hang on to every flower they can.
This year, our groves are experiencing an "on" year. That might be why we are noticing more post-pollination nut drop.