I am so curious about these guns...
The city designator seems like it makes the most sense...now to determine what DB and DP truly mean for certain. Since the fonts usually don't seem to match, I suspect these may have been made earlier, and DB and DP were added to designate their intended destination or purpose. Since they all seem to have Norinco import marks the thought of Bangladesh and Pakistan make less sense, a study into when military aid stopped to either of these countries may help...as it seems unlikely to me that if they were supposed to go there, enough of these would be stockpiled to make it to export to the US. The serial data seems to indicate they might have been made six years before any military aid to Bangladesh would have even happened....the plot thickens....
I am leaning more towards they were actually intended for domestic use....perhaps an early/alternate security forces designation? The amounts imported of those seem to be about as uncommon. Maybe the region characters represent where they were to be put into service? The DB and DP could be actual factory marks instead of destination/purpose stamps?
The intended purpose might lend insight to why they seem to be so shoddily built. One off fabricated various parts...odd parts not normally associated with the SKS. Could they have been intended for training purposes only maybe?
I also harbor a suspicion that these may be the result of student/apprentice builds...which might explain the oddball parts...and the workmanship. Perhaps the city/region designators were to indicate they were made at armorers schools in those places? Could they be experimental runs of various alternate parts to decrease cost/manufacturing time? With China being a place of mass production, the low numbers of these could be explained as student builds, using outdated/worn equipment...which might explain the rough machining on the barrels.
It seems so strange to me that the quality seems so 'last ditch' when these obviously were made long after they had already 'perfected' the manufacture of the SKS.
There is also the possibility that they just used anything and everything as far as equipment for machining parts in whatever way they could...but since the numbers of SKS's imported are so massive, it seems odd to me that they would go to that extreme to make as many as they could, no matter what the quality was....when they obviously had massive amounts stockpiled anyway.
Perhaps we will never know...but I figgered I would put those bugs in your ear.