They got quite a bit of use, going by the marks on the original stairs, but just a few years later, these backstairs were rebuilt for greater convenience, or rather they were built over. A new staircase began just forward of where the old ones had on the second floor, and descended by easy stages until they ran out of room to run. So they paused for a landing under a window, then turned 180 degrees and proceeded down to the kitchen. As they reached the landing, they were compelled to use a wedge-shaped step or two, but the new stairs were still easier to climb up or down.
The original backstairs were walled in completely, beneath the newer stairs, leaving a dead space under the lower half of the new stairs, and nothing further was heard of the hidden stairs until our sainted PO Bob began gutting the kitchen for renovation.
It's incredibly hard to take a picture that shows any of this, let alone all, but I finally have got enough that I think it gets the idea across. I've left 'em big for the benefit of anyone who really wants to see the details.
First comes the newer set of stairs, still in use, as it appears today.

From the top of the stairs today
