Todd Sand was at the 1981 World Championship in Hartfort, CT, competing for Denmark in singles. I don't know whether he competed before that. (He finished either last or second to last)
I remember hearing that Olga Vassilieva (EST) had been around since 1992 Worlds, and she was in Dortmund. 12 seasons is extremely respectable longevity. I'll have to look into Mojca.