Incomplete brass lens - value?

[vitality]

How much do you think lens will lose in value when it is incomplete? For example, lens without lens hood, it will lose 10-20% of price? Same about lens without flange or missing rack and pinion?

I'm not talking about lens without glass elements or just glass elements without barrel, it is about missing parts of lens, which doesn't affect performance a lot. e.g. brass lens hood can be replaced with plastic one or with bellows lens hood, or lens, missing flange, could be fitted directly into wooden board (well, not heavy one).

Of course I'm not waiting for precise market valuation, just personal opinion on topic.
As example:
- lens what I want to use, without flange: -20%, or -100$ (to order custom made flange); without hood: -30%.
- or, I'm collecting lenses, and if it misses some parts - I'm ready to pay maximum of 20% of complete lens price...
- or may be: if the lens is very rare, it doesn't matter much if it misses lens hood. I want it, and I'm ready to pay "full price".

[CCHarrison]

From my collectors standpoint, missing parts is a big deal even on very rare lenses. In almost all collecting circles, items with missing parts - especially important parts - devalues items pretty significantly in my experience. For users of lenses, I think the numbers would be different and be far less discounted.