Aug 8, 2009 - I have a pre-ban Norinco AKM-47S. Any idea what I have here as. Now) says as far as the serial number 'M0000664' and the reciever says.
This might answer your questions: What I did was take your question a step further, by pointing out that many Chinese AK's have the 'evidence' on the trunnion, not the receiver. Someone could theoretically switch trunnions and put it on an unmarked or little-marked post-ban receiver and claim it as a pre-ban. Most likely that won't be happening.but I thought you were bringing up that concept again.
What the others said, they are pretty much clearly marked if you do some research beforehand for what to avoid. One tricky example I can warn you of in advance is Sile Imports. The pre-bans have model names like 56s-1, while their post-ban models(specifically ones caught during law changes) are marked 1-56s-1 with the extra '1' before the original model name. Other models from Sile use this extra '1' code to denote POST-ban status regardless of what the green-toothed lying gun dealer is trying to convince you of:).