Why would it matter to have original clasp?
Some people really don't care about the clasp, that's a fact. As long as it works, a typical person won't spend much attention to it. Maybe when the watch was new, they might care if it's scratched. But very soon, they will just forget about it.
After checking the collection on hand, I found a number of the vintage I have, don't have the correct clasp, that is, not the original Seiko clasps them. When acquiring vintage, sometimes they don't come with the original bracelets or leather bands. Finding the original is particularly difficult as usually they are no longer available new. And they are usually tossed with the broken watch by the user. So aftermarket bracelets are sometimes unavoidable.
One way to solve the situation, is to find suitable original clasps and transplant it to the current bracelet. There I picked up a lot of used/broken original bracelets, take off all the clasps, restore the finish the best I can with some techniques, and mount them on to the bracelets. It works pretty smooth and you see from the photo, not only there are some un-branded clasps, there you see some fake clasps, marked with 'SEIKO JAPAN'.
Now they all look good now and most importantly, politically correct. Haha!