As i understand it, angles were between 17 and 20 degrees, however all razors were ground by "hand” on large grinding wheels so you may find a wide variation... maybe from 15 to 21 degrees.
It would be interesting to see how much variation there is, especially among the same brand/model.
But even if the razor is honed many times, wouldn’t the angle be the same as it was when new if the spine wears at the same rate as the edge?... assuming previous owners never raised the spine.