Yep, I checked ExpertFlyer and there are no D1 fare filings on SFO-PUJ and only FC fare filings. Most FC fare filings explictly prohibit routings that include D1 routes on D1 equipment with the exception of FC fares with fare basis codes YNNA0NFY (non-refundable) and YNNA0RFY (refundable) which book into J class. Here's a snippet of the Flight Application section of DL FC fare rules from ExpertFlyer which runs several pages long for all other FC fares. FC fare filings have an 'F' in second to last character of fare basis code while D1 fare filings will have a 'D' there.



Even though the J class FC fares allow the routing, there still must be married segment inventory availability in J class to book those fares. And DL always looks to zero out married segment inventory in all FC classes with that routing so it is impossible to book those J fares. The only way to potentially book them is to add a stopover at JFK (layover greater than 12 hours for PUJ). At that point, married segment inventory no longer applies (there just has to individual flight inventory in J). In addition to having to pay for the J fare, there's a $200 stopover fee and the total price is slightly over $3K.