Ok, some good news (or lucky breaks)

Three new data points from three different ravellers on three different dates, arriving at three different Indian airports (DEL, BLR, BOM).

All of then OCI holders who got OCI before age 50, turned 50, got new US passport. Have not renewed OCI (none of them knew the rule as they believed on lifelong stamp to be lifelong).

None was asked any question. They presented all three documents as usual (current passport, old passport that had OCI stamp and OCI card).

Again, "dont ask - dont tell - dont educate immigration officer" seem to be good policy (of course there could always be DP #1 at some point)