they usually are not worth a premium over the other ones either FWIW, almost never in fact.
1st production runs and pre-pros will SOMETIMES bring a SMALL premium over the std models but this usally is not how it works out, same for prototypes, i used to collect BM proto's and pre-pro's and unless they are different than the regular production run in some way (ie the prototype BM 710 had a alloy vs G10 handle for example) they dont bring much if anything extra, one which is different MIGHt bring a small premium, like $25 or so, maybe a tad more, really only the prototypes are gonna bring much of anything, almost all the 1st pro run and prepro's i have seen probably ran +$5 or $10 over a std model, if that.
why? imho they make too many of them, they simply arent rare.
for example BM makes 300 or 400 prototypes while spyderco might make a dozen, thus the spydie proto's do bring some $$, as they are kinda rare if ya make 3 or 400 of a model they simply arent that rare. also emerson proto's are all hand made and number like 6 or 8 usually again they bring a premium unlike the BM's.
of the dozen or so BM proto's i had only one a couple sold for more than a std model and they both were quite a bit different than the production ones, the 710 and the stryker FWIW, the 710 with the alloy handles vs the productions G10 and the strykers blade grind was different and the handle was a little different too, some like the prototype 800's were exactly the same as the productions FWIW.
i did enjoy collecting them though, and like i said i bet i have had a dozen of the things thru the yrs & still have a couple of them.