Difference between some xpacs?

Hi,

I'm pretty new here, well been here since 2012, but haven't really played...

I'm wondering what is difference between xpacs:
- WotLK and WotLK (old) and
- MoP and MoP (old)?

Just so I know what I'm downloading.

Thanks guys!

the (old) ones contain the models for their respective patches. the non old ones are wod models.

is there any way i can see pre patch events... like event of pre WotlK?