analizing mirror tests

I don't know if anybody here searches ebay for telescope mirrors, but recently there has been some "professionally made" 8" and 10" mirrors with full test results listed including PV wave measurements (usually around 1/10 wavefront). Graphs and numbers go on to say .98 this and 1/50 RMS that, but at the end of the page is a disclamer stating that the measurements on the box (from the factory)may be lower than what appears in the above data, due to a testing program that uses a cubic spline regression instead of a straght one. Apparently the same raw test results were used, but they were plugged into different programs. I spoke to someone who bought one of these mirrors and he said the box read .86 strel when the auction read .98 :S . Does anybody know if these different focault testing programs could actually give such different results?