I'd count Simon Edge and WingsoverScotland as GC and both say it's them, as do a lipreader and an audio editor with 40 years' experience. He also says them at the start to refer to JKR and IW collectively and it's identical. It's a sociolect, close to "em", so the TH mouth movements are neither here not there. He's of an age where he uses gender-neutral pronouns pretty fluidly. I mean, it's not a hill I'm going to die on I'm saying what I (and other people[ heard, not what I expected to hear.