evidence collection guidelines

Hi

I have some questions that I hope you helpfuls can help me with.

1. why is there a need for universal evidence collection guidelines?
2. What is wrong with current guidelines used?
3. is there any major differences between them?
4. why isnt there any universal evidence collection guidelines?
5. why isnt such guidelines like the g8 principles followed? isnt that universal?

I know these questions are a bit direct but if i can get any helpful response that would be great.

thanx