I’ve seen a lot of posts concerning FG for a given yeast. This is my perspective on tolerances overall for the hobby.
Each style has a starting and finishing gravity, bitterness, color, alcohol by volume, carbonation level, etc. tolerance or range. Some are very narrow and others broad.
Variability exists within our brewing systems, the weather from brewday to brewday, the water source, and on and on.
Given that we are hobbyists, we use agricultural products with variability from field to field and season to season, and most don’t have access to sophisticated laboratory facilities, we have to estimate the finishing parameters of our product.
We use various calculators, spreadsheets, and software programs based on models and formulas to help estimate the math quickly so we end up with a predictable result.
Generally speaking, if a homebrewer aims for the middle of the style guidelines, using a reasonable approach to recipe design, they will land in acceptable ranges for the various parameters and make a good to very good beer that meets the style guidelines.
However, all these variables can stack up so if a brewer has elected to brew on the high or low end of any of the allowable parameters for the style, it could result in an unbalanced, unpredictable result if any one or more of these variables are incorrectly estimated or executed.
My recommendation to the brewer who is concerned with the exact finished gravity of their product; considering all the things that are estimated, modeled, predicted, and hoped for, as long as the end result is within the guideline parameters for the style you’re good.
Sure, we want this to be exactly as we predicted but truth of the matter is when dealing with Mother Nature, human error, and all the variables involved, we’re pretty fortunate if we land within the guidelines.
What I do: aim between 50-66% of the style guidelines for original gravity, bitterness, color, and ABV based on carefully established equipment setup in my software of choice. That way, if I boil a bit too long, or don’t get 100% extract from my grain, or I was a little over/under on water volume, my hop AA wasn’t as predicted, the particular grain I got was a little darker than advertised, I misread the hydrometer, etc, etc… I’m still OK. I can be off +/- 5% or more in some cases and still be within the style guidelines.
Likewise, using the mfr’s prediction for the yeast attenuation (e.g. 71-80%), base your estimated FG on the middle of the road AA (in this case ~75%) and if it comes in higher or lower it’s not an issue.
I guess the point is use the tolerances you are given w/o expectation of perfection. Close enough is good enough.