SIX revisions? Hopefully only metal layers, or were some a full base spin too?
Where I work, we usually go into production on the second revision. Occasionally, the first one is good enough (usually if it's similar to a previous chip). The one I worked on most recently was a brand new design from the ground up with a new team of people, so we shipped the 3rd version (both spins were just metal layers). We (almost) never change the base layer - the case I heard about was when somebody in Marketing told someone in Engineering that there was no way they'd ever want to market a specific part to use >n MB of memory (probably 512 or so), because it was a low-end part. So they put enough address bits on the part for 512 MB - and then not too long after making it, Marketing decided that they needed a 1 GB version too. Then it just became a question of "is it worth a million dollars to be able to sell it with 1 GB?"
I'm in verification, so my whole job is to make sure we haven't made any million dollar mistakes. I produce no useful output, other than a thumbs up to management right before they start producing wafers. Some mistakes still get past us, but when a million dollars is on the line, some creative changes (often just in software) can help us keep the problem at bay.
And any time a big mistake gets by, another item gets added to our checklist. Being the first guy to make a particular mistake is usually professionally survivable; everybody makes mistakes sometimes. But being the second guy to make the same mistake does not bode well for your future...