Trident used for A Night at the Opera... legal issues

Back when 'Opera' was released in 1975, they didn't mention Trident Studios being used for recording or mixing, although they had been (for the National Anthem). The omission was corrected for the 2005 re-issue but, considering everything, couldn't/wouldn't Trident sue them for ignoring them in the credits? Or are artists allowed to do that?

Maybe there was a clause in the severance agreement that said Trident couldn't counter-sue for anything?  But I'm no lawyer, so I haven't a clue really..