1453 was the date Constantinople fell. It was the capital of the Eastern empire. The Western empire, whose capital was Rome, fell in the fifth century.
But my point was, it was still the Roman empire. Or so they considered themselves.
STill, it’s a quibble. What 70 year period were you considering?
For myself, I think the end of the Roman people coincided with the beginning of the Roman Republic. Like a snake with its head cut off, it continued to writhe for a while.