Question about fermentability and attenuation

As I read about going all grain, there is a lot of discussion regarding the fermentability of wort and the fixed fermentability of extract. Then there is also the ability of yeast to attenuate. I just want to make sure I have it all straight. For example if an extract is fixed at 75% fermentability and you get say 77% attenuation, does that mean that of the 75% of the sugars available to be fermented, the yeast successfully got to 77% of those? So if you brewed the same beer as an all grain version and mashed lower and got a more fermentable wort, the same 77% attenuation could actually "eat" more sugar? Thanks for the help.

I'll let some of the more senior members chime in too but the way I understand it you are correct.

borealis said:

So if you brewed the same beer as an all grain version and mashed lower and got a more fermentable wort, the same 77% attenuation could actually "eat" more sugar?

Click to expand...

Yes, in that the 'more fermentable' in the case of all grain mash temp variables means the presence of more simple sugars (or fewer complex sugars) as I understand it.

Thanks for the replies. It may seem like a simple question, but I just wanted to make sure I was thinking of it correctly.