It's possible (probable) the laser/lens pickup is not tuned for the relectivity of the dye used in dvdr's (purple) but is fine with silver ones (pressed). This was the case with early expensive CDDVD players such as Sony's - many were great with pressed discs, but until udal pickups came along, most could not play burnt media.
Most cheap players these days can cope with almost amything, as long as the media is good enough. Incidentally, if your discs were really dire, or the burn, then even those you kept may drift and be much worse some months after - this is the worry regarding media longevity in other discussions.
Posted after I got back to the PC - I did not see the earlier post regarding pickups.