Hi Togel:
I mean no offence, but "extremely common" is a relative term. Where you live, kangaroos might be referred to as extremely common. Where I live camels might be extremely common. We are, after all, on the internet.
I received about one year ago, a mailing from the American Institute of Structural Steel Detailers. (I hope I have the name correct.) I threw it in the garbage, so I can't refer to it at the moment. The crux of the document was a plea to structural engineers to produce better drawings. I was so upset by the document I couldn't bear to keep it. Like you, I have seen far too many "fuzzy" drawings. Where I live "fuzzy" is a common term. Far too common.
In my work, I get to see the product from many different design offices. As a structural engineer it pains me when I see fuzzy drawings. If the structural engineer can't be bothered to show the deck support angles, why should the fabricator be obligated to supply them?
I have been in your shoes. When I said "missed some steel" it was a bad choice of words. Of course you cannot miss steel that is not shown. The reality is many designers are not painstaking when it comes to their drawings.
You ask: "should the contractor overbid because he thinks the designer has done a lousy job?" The answer goes either way, depending on your situation.
When I was younger, when business was slow, the fabricator I worked for used to prey upon designers who produced fuzzy drawings. He knew there would be plenty of extras. So he bid low knowing there would be a lot of extras. Not a nice way to make a living, but it put bread on the table. (I will never return to those days.)
When you are busy, and don't really need the work, then (and this is just my opinion) you should give the fuzzy designer a much higher price. Where I live this is "extremely common". If he later says, "Oh, I need a deck angle here and one over there.", then you can smile and say "No problem, what color would you like?"
Rpoche gives good advice: submit a detailed explanation, and a quotation. Don't do the work until the matter is resolved.
You say it is becoming standard practice for designers not to provide top of steel elevations and dimensions. That may be true, but it is not a practice I would ever be a part of.
You suggest that a designer is not rewarded for producing good documents. I disagree. If you're not giving better pricing to better drawings, maybe you should consider that.
Now I'm rambling.
The sad truth is the owner will NEVER know how much more it is costing him because of fuzzy drawings. The only way to understand the cost would be to have 2 separate designers produce drawings completely separate from each other. One designer is known for his fastidious, painstaking work. The other is renowned for his use of a spray-painter. Then get the contractors to price each set.