IMHO I suspect that every president alive has classified documents in his library. All should be investigated if one is investigated...
You're absolutely right. 10-1 Bill Clinton took plenty of classified documents with him when he left the White House, and then there's Hillary who sent classified documents through her personal email account. She also advised State Dept. aides who claimed they were having problems sending documents with classified headings, to strip the headings off, and send them that way, even on an unsecured network. Then of course, there was her sending classified documents to her maid at her Washington residence, so she could copy and collate them for her.
Did Hillary Clinton Ask Aides to Strip Classified Markings Off a Document