edit What problems have you encountered?
If your scans with the 1640 are generally consistent from scan to scan (re-scan to be sure..), this is bad news for your discs as not only the PIE levels have doubled but the total PIF count has doubled as well! Such degradation in to weeks may only be due to defective discs, unless you store them in bad conditions (light, heat, humidity, dust..) - how do you stock your discs by the way?
Another thing to consider is: are your 1640 scans generally consistent from scan to scan? I have no experience with the 1640 so I don't know much about variations in scans with this drive. I haven't been consulting the Benq forum much since my 1620 died.
Re-scan and see if your result are similar, just to be sure :iagree:
As to "fakes or not fakes", I'm enclined to trust Dakhaas in this , so if you discs are indeed degrading and keep on doing so in the next weeks, you should have them replaced through Verbatim's warranty.