Trump had been taking documents out of the White House for the last year of his disastrous reign.

[kentuck]

7. Another link that may help with the time frame that he started hoarding the documents?

From January 2018:
https://www.marieclaire.com/politics/a15344714/donald-trump-white-house-changes-renovations/



(snip)
Through interviews with current and former Trump aides and advisers, Wolff also discovered that Trump had asked that two more televisions be installed in his bedroom (which means there are currently three TVs in his room) and that a lock be added to his door, an act that “precipitat[ed] a brief standoff with the secret service, who insisted they have access to the room.”