My simple understanding is that although damaged beyond practical repair, with machinery thrown out of line etc. The British didn't know it and therefore, to them, Tirpitz still remained a "fleet in being". I have heard that the crew that hit her on the bows with a tallboy was not believed when they claimed the hit.
There was apparently a Norwegian report at the time that said the ship had been hit in the bows but the extent of the damage wasn't known.