I'm at the tail end of a large project (around 5 months of my time, > 60,000 lines of code) on which I was the only developer. The specification documents for the project were designed well early on, but as always happens during development, some things have changed. For example:

• Bugs were discovered and fixed in ways that don't correspond well with the spec
• Additional needs were discovered and dealt with
• We found areas where the spec hadn't thought far enough ahead and had to change some implementation
• Etc.

Through all this, the spec was not kept updated, because we were lean on resources (I know that's a questionable excuse). I'm hoping to get the spec updated soon when we have time, but it's a matter of convincing management to spend the effort. I believe it's a good idea, but I need some good reasoning; I can't speak from very much experience because I'm only a year and a half out of school.

So here are my questions:

1. What value is there in keeping an updated spec?
2. How often should the spec be updated? With every change made that might affect it, just at the end of development, or something in between?

EDIT to clarify: this project was internal, so no external client was involved. It's our product.