Because Biden's lawyers were the ones who initially discovered the classified documents, it would make sense for a prudent and responsible lawyer to gather all facts before unleashing a story to the press for folks like you to conjecture. For instance, assume Biden was not the person who packed up his office as he departed the Vice Presidency in January 2017. Assume he delegated to one or more than one assistant. That person is entitled to notice and entitled to counsel. It would be reckless and irresponsible to "go public" and unfairly throw an assistant under the bus. It may be that is unknown who packed up the Vice President's files, or unknown at which point classified files were intermingled with non-classified documents. It may take some time to gather that information.
It has not been established that Biden was aware that he was in possession of classified documents at any off campus locations. Hence, he had no knowledge nor likely any inkling. So no, it is not a situation of searching for drug paraphernalia that may be in the attic or basement on one's first day of probation. If Biden never had reason to believe that classified material was intermingled with his other stuff, then not sure why he would think to look. If he had some notice that it was plausible that documents were intermingled, then prudence demands that he should have double checked asap.
Biden (through his lawyers) did make a timely disclosure. No credible source has suggested otherwise. There is zero suggestion that Biden has endeavored to conceal the documents or play keep away.
You keep suggesting yesterday's discovery/disclosure is the "smoking gun." It is not. And I am 100% confident that the Special Counsel will not treat yesterday's discovery/disclosure as significant. Rather, the Special Counsel's focus will be on (1) the original intermingling of classified material with non-classified material and (2) the failure of the Vice President's office to uncover the misplaced classified material thereafter. That is, whether Biden knew or "should have known" that classified material was misplaced and intermingled will be the focus of the investigation.
And notice that none of the Biden supporters on this Board have posted that this is "nothin burger."