The caveat of carrying the old passport with you is now a standard sentence:
As and when prohibition on international air travel is lifted by the Central Government and the status of OCI card as a lifelong visa for travel to/from India is restored, such OCI cardholders may be allowed to travel on the strength of their existing OCI cards bearing old passport number. However, this will be subjected to the condition that the OCI cardholder will have to travel along with old and new passports and the OCI card having the old passport number.