I looked at the extract potentials at http://www.tastybrew.com/forum/thread/113723
and they seem normal.
There is a separate brewhouse efficiency of 77% in the recipe. There are three parts to brewhouse efficiency: (mash) conversion efficiency which can approach 100% for homebrewers, lauter efficiency which is generally hard to get over 90% for homebrewers because the grain bed retains a lot of wort, and kettle (?) efficiency which is dependent on how much wort you leave in the kettle for hot break and hops.
To quote Palmer "The [brewer's] extract efficiency is dependent on the mash conditions and the lautering system." Extract efficiency is equal to the first two parts of brew house efficiency.