Originally Posted by
jdrtravel
...........The real issue seems to be that you booked a really tight connection, and one that is very unadvisable when needing to change airlines and terminals. Complaining about not being told about checking in at JFK seems, to me, to be you just looking for a way to get Delta to fix the real issue, which is that you booked an irresponsibly tight connection, and don't want to pay to fix it. Luckily, your medallion status + having a separate domestic ticket entitles you to a free (domestic) SDC, so that is where you should focus your energy.
MCT for DL-MU connection at JFK is 1:40. OP seems to have booked two separate tickets to change in JFK for 1:57. It is very tight but doable if all goes well. As others posted, luggage can be checked through, the only issue is to go to MU check in desk to get boarding pass. MU doesn't allowed self-printed boarding pass from USA anyway. Even if OP were able to OLCI, he/she still need to go to MU check in desk.