From all the photographs I've seen, the operators of stamp perforating machines were nearly all young women. Not sure why, but maybe it was considered on a level with telephone operator or other middle to lower-level service jobs.
And the machines they used to feed through long uncut sheets of stamps were more like large sewing machines with lots of hollow "needles" compared to the much more reliable, sophisticated and smoother operating machines we today.
Compare today's car factories with the car factories of the early 20th century. Today, robotic machines relaibly form panels and carry them to the cars to be welded onto the cars robotically. Result? Fairly perfect auto bodies. Back then? Some guy took a sheet of metal and using a hand-operated metal press, he pressed it into something resembling the shape of a fender. Then, he picked up his hammer, put the panel on top of a bag of sand and began to beat the panel into the correct shape. It's absolutely amazing auto body panels turned out as good as they did compared to today.
And you could do the same thing for eyeglasses, shoes, books (hand-made mostly back then), and most other things. That perforations ended up at all straight is kind of amazing given that some young lady was wrestling a large sheet of stamps through a machine that seemed to want to rip it to shreds and it came out the other end in good shape but with holes "pretty much" between most of the stamps. I'd guess they threw away the more catastrophic mistakes, so we end up with halfway decent perfs on most stamps. Except for a lot of the stamps in my collection where the perfs go right through the designs!
Have a look at some of the older perfing machines here for a job that took a lot of dexterity. https://images.search.yahoo.com/sea...ges&fr=yfp-t