What was the "Northeast Corridor" called prior to Amtrak?

Does that name pre-date 1971?
If not, what was the electrified PRR/PC mainline along the Eastern Seaboard called back then?

I believe it was at one time the NewYorkCentral, either that or the Pennsylvania Railroad, NY to DC

i think it was always the NEC

I don't know about names, but the former Pennsylvania Railroad portions were the: New York Division, Philadelphia Division, Philadelphia Terminal Division and the Maryland Division.

The NEC was established between the 1830s and 1917.
https://en.wikipedia.org/wiki/North...ilroad (PRR) between New York and Washington.

The included lines even then were: Pennsylvania from Washington DC to New York City Penn Station. Connecting from Penn Station via Hells Gate Bridge and up through New Haven and Providence to Boston, was the New Haven. The NH switched from electrics to steam, later diesel for the remaining run from New Haven to Boston back in the old days until that portion was electrified in the late 1990s.