Do they ever learn?
I was just two days into an MOD contract and opened the "XXXXXX Specification Document". There were lots of pages marked "this page intentionally left blank" and paragraph sections with TBA in them.
It was reminiscent of the Blackadder scene where they are planning to go around the world. Melchett says: "“Blackadder, here’s a map of the known world (hands over blank parchment)… fill it in as you go along”"
On my project I was given a fairly complete section to code and told not to worry about the rest for now. At every point where an API call was required I made something up and updated the specification document. It was coding by the serendipity method.