I recently contacted Bushmaster about a lower I had purchased that, by all sources I could find on the Internet, checked out as a pre ban. My hope was to have them provide me with a definitive determination and maybe even a letter certifying it was in fact a pre ban so I could tuck away just in case there was ever an issue. As you know Cerberus acquired Bushmaster several years ago moved the company from Windham, Maine to Remington in Ilion, NY.
The response I go back by email was a bit surprising. They said the serial number I provided was likely in the pre ban range. However, they said that when the company was moved they didn't get all the manufacturing records from previous years so they couldn't say for sure whether it was pre ban or not. I suppose BATFE must have a copy of those records. But if not and the issue ever came up in court during a criminal proceeding about pre v. post ban things could get interesting since it seems even Bushmaster would not be able to provide an answer.