I don't believe it.
I'm usually in the 83-85% range for mash efficiency for moderate beers depending on my recipe, and sparging method/process. I can get in the 88-90% range if I want to, but the amount of time to do so isn't worth the effort in my opinion.
Some of the past posts have stated they get a "constant efficiency" This is just not realistic and is a mathematical impossibility. Your mash efficiency is going to vary depending on a ton of factors, but mostly due to your recipe, ratio of first runnings to second runnings, and total water needed to grain bill. Larger grain bills, all else being equal, will have lower mash efficiency.
This is a fact, anyone claiming otherwise doesn't measure accurately or doesn't understand how to calculate their efficiency.
You don't want to get a constant efficiency, unless you plan on brewing the same beer ad nauseum, what you want is a predictable efficiency. To that end, I don't think anyone has given better advice to that point on these forums than @doug293cz, although Gavin and myself are probably the next most knowledgeable in my biased opinion.
For simulations on your equipment for batch sparging and no sparging (fly sparging simulations are hard) , you can use my mash/biab calculator located in my sig. Give thanks for the mash analysis numbers to doug, he did the grunt work, I just put it online in an easy to use format when I combined it with my calculator.
Since I started using dougs simulations, I haven't been off on my OG by more than 0.002~ and that was because I boiled off slightly more than intended due to the finicky controls on my burner.