If skonto is possible (skonto_date exists), add two possibilities:
without_skonto and with_skonto_pt if payment date is within skonto_date,
preselect with_skonto_pt, otherwise preselect without skonto.
If skonto is possible (skonto_date exists), add two possibilities:
without_skonto and with_skonto_pt if payment date is within skonto_date,
preselect with_skonto_pt, otherwise preselect without skonto.