Nineteen-teens to early 1920s.
This one takes the Unsung Sewing Patterns award for Justly Forgotten Economies. I can think of few sewing tasks grimmer than cutting down old stockings in order to sew them up again.
That said, this pattern raises some interesting questions on clothing usage. Did people re-use only stockings from their own households, or could one buy used stockings for just this purpose? Was it considered acceptable to use single stockings and match them up as best one could (easier with black, of course, than with tan or other colors)? Did ladies do this as part of charitable work to provide clothing to the poor, particularly for children?
According to Clothing - Choice, Care, Cost, published in 1920, the cost of hosiery in general almost quadrupled during World War I. The "make do and mend" efforts of World War II are still well known to us, but this pattern may be evidence of the same type of effort during the previous war. This book also mentions that factory seconds stockings could be purchased inexpensively - these may also have been candidates for cutting down.
Although the instructions indicate that the stockings could be sewn on the machine, I think machine stitching would be heavy-looking and would be uncomfortable, particularly in the feet where the rather stiff seams might rub.
The envelope indicates that this pattern could be used for re-footing stockings, but the instructions themselves are silent on this point.
This is an unprinted pattern.