BTW if the spokes are not perfect, or the fit of the spokes is bad and/or the wheel/spokes are not stress-relieved adequately, you may experience spoke breakages within 1000 miles (eg in a rear wheel).
If the spokes are badly made but the fit/stress relief are good, you may not experience failures so soon, but (in contrast to a wholly good wheel) you will experience spoke breakages, and they will carry on happening (randomly) for ever, or at least until all the faulty spokes are changed for good ones.
Thus if you break more than one or two spokes in a wheel that should be 'good' (because you have used good quality spokes that fit well and have subjected the wheel to thorough stress relief, e.g. Brandt-style) you have to be suspicious of faulty spokes.
It is usual for all the spokes in the same box to be made on the same machine at the same time, so if some are faulty they should all have the same fault. The exception to this is if the J-bend die is badly lubricated and is subject to galling; occasionally an adhered lump of crud on the die (which has been ruining the bends on the previous few spokes) will detach and the next few spokes after that might be OK, or better at least.
But if you find a faulty J-bend in a single spoke in a wheel, it is probably best if you replace all the spokes of the same length (i.e. that came out of the same box originally) in that wheel.
FWIW I've bought and used many thousands of DT spokes over the years (NB in factory sealed boxes, i.e. not ones that have been cut and rethreaded, which is all you will get in some territories) and they have been very consistent in quality. The only exceptions to this are
1) sometimes a full box will manifest a (functionally harmless) slight ripple appearance (eg in the width of the central part of a butted spoke) presumably because the swaging has not been perfectly applied and
2) two or three times the box has contained one or two spokes which are unthreaded.
3) the butted lengths are sometimes not perfectly consistent box-to-box
So I'm not complaining, except perhaps at the prices that are usually charged for them....
Sapim seem to be similarly consistent; I've used fewer of them myself but a local builder uses many thousands a year and he reports to me that there have been few if any problems.
cheers