Can an Uber driver drop off passengers in NYC if he is registered elsewhere (i.e. without a TLC license)?

Yes, drivers can drop off in NYC without TLC license. TLC's State Reciprocity Statute applies.

Yes, any drivers, with or without TLC license (i.e. the permit to pick-up in NYC), can drop off passengers in the five boroughs of New York City. Even if are registered and regularly drive in NJ, you are still permitted to drop off in NYC.

This is outlined in TLC's "State Reciprocity Statute."  Notice the third bullet, where it states "All vehicles could drop-off passengers in New York City or transit through New York City"

(source to TLC's doc)

Related article:

Can a Uber drive operating and driving in New Jersey (NJ) pick up in NYC or New York State?

Can I drop off at Newark NJ and pick up? (as a NYC driver)

Drive uber with NY licence in New Jersey

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Uber Driver, CEO of TaxiFareFinder and Unleashed, LLC