That's why you get the people who give you the requirements to sign an Affidavit.
Except for the fact that in many cases... those same people are those who sign your paycheck (in the case of internal development).
Heck... at an old job years ago, we used to joke that "We could have Al sign off in blood on a set of requirements... that wouldn’t matter a week later"... Al being the president and co-owner of the company (the other owner (and brother) was head of HR).
Granted... this was a company I left eventually in part due to a a disagreement over a ‘contract’ which involved a piece of paper which had a set of terms and conditions... my signature, that of the department manager, and that of the president... which
HR referred to as an 'implied contract'.
(Grrrr... this reminds me that I've once again (for the 3rd year in a row) forgotten a new holiday I plan to start... 'implied contracts day' which is to be celebrated on March 1st)
Unless you are dealing with fully external entities who sign off on something and with enough contractual verbiage to enforce said sign off... most projects are rather easy to have shaken up and radically changed dang fast.
Edit: Wait a second... HC... I understand why you don't have the C9 tag at the bottom of your post... but have you left MSFT? Or has someone on the C9 team opted not to tag you as a 'softie without warning yet (as they did me).