I began practicing law just after the District Court's e-filing systems, CM/ECF and PACER, were implemented—so I didn't get a lot of experience with how attorneys used to manage federal dockets or handle federal filings before you could just instantly file or pull things.
But occasionally, when I'm researching something, I'll find a reference to a document that looks helpful but that was filed before PACER existed, and as such is not available in Lexis or Westlaw. Typically, my response is to look longingly at the citation, and then to continue searching until I find something …