Forgive Barret Jackman for his ignorance, but in the late 1990s the Blues’ defenseman knew little about the significance of the No. 5 and its original owner when it was handed to him at his first training camp. “You do your research but the Internet wasn’t that big then,” Jackman said. “Right away, I talked to Kelly Chase and he was very eager to tell me the story of Bobby and what he meant to the organization. I was in awe when I heard.” An original Blue on the 1967 expansion team, Bob Plager has been with the organization as a player, coach, scout, confidant, ambassador and resident joke-teller. He’s thrown more hip-checks, given more trade advice, shaken more hands and delivered more punch lines than anyone in the history of the organization. Until last week, Plager also had the distinction of playing in more games than any defenseman to suit up for the franchise, a list that included his brother Barclay, Al MacInnis, Chris Pronger and so on. But when Jackman, wearing a Bluenote on his chest and No. 5 on his back, joined the play at 7:08 p.m. Saturday night against Columbus, he climbed atop the list with game No. 616.