glitchbirds can you go back and get them?

[AerialComb]

I read somewhere that if you miss even one you have to restart the whole game, is that true?

[Cyber Akuma]

It used to be true but that's been patched, I recently went back and got them all, it was the last achievement I was missing. It's just that some of them require you to replay large chunks of the chapter to get them (And don't forget that you can't save in chapter replay mode).