If you want a comprehensive guide on this campaign, bugs, shortcuts, secrets and all that good stuff, check out this guide:
https://gamefaqs.gamespot.com/pc/960510-left-4-dead-2/faqs/74712
The Man who created it, is probably even more obsessed with this campaign than I'm. So if you want to get all the possible info, this is the way to go.

It is updated accordingly with all the changes I make to the public version of this campaign, so all the info included shall stay relevant till the end of times.