Company that is not up to date on it's SEC filings still shows trading volume of the stock. Who is trading them?

This is a very strange request but I am not sure where to find the answer. My grandfather and I were talking stocks the other day, and he mentioned that he has a boatload of shares in a company traded on OTC markets that does not have up-to-date SEC fillings, but the stock still shows that there is trading volume on a daily basis. Who is making these trades? As far as I'm aware, he's just a regular retail investor, but I am curious in this case if he'd be able to work with one of those firms who can still make those trades.