okay....
I'm from that area and i have smoked a ton of that "asian" bud in the past... called asian bud because it was the mass produced bud by the asian mafia... the triad.. and it was the standard cheap "hydro" you could get from all the dealers.. It was bright green, covered in crystals, but the taste and smell was noticeably different from the other mass produced strains around at the time.. At that time there was rumours that this guy or that guy has northern lights #123456789, but it was never enough to make an impact on the market to be available to most dealers at a competitive price to the triads cheap hydro that "did the trick".
Now on to the headache.. yeah i did get it, often enough that i wouldn't buy that bud....if i could help it.. when you jones you jones.. lol... Was it due to the growers not flushing their weed? possibly, but it has so many other factors.. I believe they just grew their bud too long trying to get a larger yield with little to no care on the effect on the quality of the bud.. causing the bud, over ripened, to give that couch lock feeling that, if smoked too much would end up in a headache.. and burnout..
Now, people now days do grow and don't flush... they may get better bud from flushing, they may get better taste from the bud when they flush, but there is not, at least i don't believe, a direct connection between headaches in weed and growers not flushing the medium.. because there are so many other factors that can cause headaches from smoking marijuana.. like strain, grow time, curing, flushing, over fertilization etc...