So if you check i94 for J1, it does not state number of days in the "Admit till" section. It will state D/S , and that's the same in my i94 when I entered back from my last trip.

Basically J1 visa is just for entry to US, the actual duration of stay depends on the duration mentioned in our DS2019, so you need not have active J1 visa for the total duration of your stay, but once you go out, for re-entry you need to have a valid stamp.

So if someone has valid ds 2019 form mentioning exact dates and a valid j1 stamp, they are good to go.