It seems in EA's ultimate wisdom they sent the UK english version of celebrations to Australia instead of the US english version. Besides changing the clock to 24 hour time, seems it can also alter names. I know that this isn't something new to people who have used mixed packs but whereas there was a fix by changing the registry this doesn't work with Celebration pack due to their being no US-en support files for it to switch too.
I know backing up your game is a recomendation in any case before installing an expansion, but I stupidly had become complacent and not done so (especially considering this was just supposed to be stuff) and consequently have lost months of gameplay. Changing the names of the pets in game wasn't an option because when I went to do that the game seemed to think they were plant sims not pets. Who would have thought