Brett, I have some of the late and a couple of "I ain't sure" ones also, thanks for the help/advice..
You mean, they are 25LAs? You have never actually said what engine you are talking about here...
The test for the 25LA "late" and "early" versions is to run them on the ground, put on an APC 9-4, and peak them out lean. The "late" engines will spin up pretty easily to the upper 13,000 to 14000 range, the "early" will be in the upper 12,000s at most.
All the "early" engines we have had were blue, all the "late" versions were bare metal. That doesn't necessarily mean that there aren't good blue ones, or weak silver ones, just that this is what we have found so far.
Brett