I still haven't figured out when the girls took off part of their blue costume. It seems that in America this happened before the encore (as there are pictures which look like they were taken from a performance of HIYS where they already got rid of the tops. However, in Wembley they wore them up until the encores – they still have them on during Dancing Queen and only took them off for Waterloo (if we assume that the short clip of Waterloo was recorded the same night as the other footage which I somehow doubt). I must admit I don't like the blue costumes with the tops on, they don't look very flattering. The final costumes that are a blue copy of the white ones they wore during the first part look much better although they sometimes reveal seat stains in some "Interesting" parts
^ I find these photos really fascinating since I was working on making these costumes for my dolls and never did fully understand how they got into the outfits. XD Also I could never get any good clear shots of the outfits, so these are quite helpful. Thanks so much for sharing tyra71!