I'm sorry you ran into this. It does seem that things have changed and the procedures tightened up. For years I traveled with the old and new passports and without getting the OCI reissued, and it was totally fine at all points, no problems with (many different) airlines nor with BoI. However, as we know, from last year the 50-years rule started becoming more tightly enforced, and on my last two visits to India I did have the BoI officer suggest that "it would be better" to reissue my OCI booklet - even though I strictly speaking still did not need to. Which seemed odd, at least they could stick to their own rules. Anyway, the next time I travel to India I will have updated documents on hand, as I'm taking advantage of the pandemic-induced break in my travel to renew my passport and then I will have to renew my OCI too (by the 50-years rule). Hopefully there will not be further problems in this area for a long time after that.

Of course, now the next thing we might run into is whether anything will change with the renewal process and rules now that Cox & Kings is out and VFS Global is taking over US visa operations for the Indian missions from November. Hiopefully they're just as (in)efficient as Cox & Kings and renewals won't take longer nor the process become more cumbersome.