I've done it a few times.
Once was the first/only time I saw Halford and they had Primal Fear opening. When Primal Fear got on stage I was really confused because they looked like what I was expecting Halford's band to look like, and they sounded like it too. It wasn't until close to the end of their set that I finally figured out they weren't Halford. When Rob actually DID go on, of course, it was UNMISTAKABLE, but I had not seen either band previously. ....OOPS
When I saw Children of Bodom with Hypocrisy, my friend thought Hypocrisy were COB.
Once was the first/only time I saw Halford and they had Primal Fear opening. When Primal Fear got on stage I was really confused because they looked like what I was expecting Halford's band to look like, and they sounded like it too. It wasn't until close to the end of their set that I finally figured out they weren't Halford. When Rob actually DID go on, of course, it was UNMISTAKABLE, but I had not seen either band previously. ....OOPS
When I saw Children of Bodom with Hypocrisy, my friend thought Hypocrisy were COB.