Well, that has nothing to do with the canonicity of Op4/BS, since Opposing Force and Blue Shift were made after Half-Life. They could hardly have recalled all HL1 games just so they could put Barney without his vest and helmet and Shepard in!
They were retconned in, just like how Eli, Kleiner and Magnusson were retconned in after HL2 was released. VALVe didn’t know at the time who any of these characters were, after HL2 was released they simply said, this black guy is Eli, that white guy is Kleiner and the casserole belonged to Magnusson.
If you don’t want to accept anything that wasn’t in the original HL1 as canon, then you can’t accept Alyx or ELi or Kleiner or Magnusson as canon either.