Yes and no...
It is easy to ‘touch’ a file, changing the creation/modified date. Some types of files also contain metadata -Internal invisible tracking of editing, which could expose such a fraud - most methods of touching a file would not alter said metadata. But, it is also easy to wipe or alter metadata, if a file does contain it. There can also be change logs in the OS the files were modified on, or on the internet server they were uploaded to. However, these too are easy to change/wipe providing one has access and authority. One can also determine how the file was saved to the drive - But this too is easy to fix, by defragging the drive and mft, and wiping free space.
What you are trying to do is catch somebody who doesn’t know how to change these things... If it is professional IT with full control, you are probably boned.
One way or another, you need a lawyer and a forensic computer specialist to find out. lots of bucks to chase this bet... Better be worth it.
Since it’s a domestic government website, I wonder if other copies are archived at Library of Congress, National Archives. WB machine supports my contention, but it is sometimes inadmissible. I wish I could be more specific, but if there’s a settlement, there could be non-disclosure.
I would have to say that all the comments have been quite good, and I’m impressed.