Hi Nick,
I recommend using the Date Sort variable, {datesort}, in the folder name field. If your Ingested images don't have an IPTC date set, then the IPTC date variables shouldn't return anything. The Date Sort variable returns an 8 digit number with the following format : YYYYMMDD, based on the image capture date. I tried using your IPTC date variables in the folder name field on my X.6.8 Mac with PM v5 beta 2 and it does use the correct date from the variables. You might try re-installing the PM v5 beta to see if this fixes the problem. If not, then use the Date Sort variable, {datesort} in the Ingest dialog's folder name field.
regards,
--Bob