If I couldn't be sure if the document was authentic, you can be sure I'd want proof of authenticity from the court before I complied. Throw the book at me if you like, I will present my case to the court. If it was proven that the department were issuing fraudulent subpoenas, shouldn't we treat all their subpoenas as questionable until proven otherwise? It seems like a perfectly reasonable response. Of course, IANAL and TINLA applies.