In the old days people had to rely on reading about a show when it was advertised in a print ad, flyer or mentioned on the radio, it's not like the club or bands were making personally phone calls to every fan that might be interested in seeing the show.
Prior to introduction of soft sales, all new 9:30 shows were annouced on the website to the general public the day tickets went on sale. Which by the way occurs 9 times out of 10 on a Thrusday. A weekly email is now sent out Weds annoucing any new shows. Bands provide tour dates to fans via web, email, etc. Pollstar and other websites have concert information available.