From what I can tell from this discussion, you are talking about using these blocks for daily machine tests, and the NVLAP blocks for your bi-annual calibration process. If this is correct then I don't see a problem in using these blocks. From the daily test standpoint the primary requirement would be getting consistent results, not necessarily "accurate", thus there is not the necessity to use the expensive NVLAP blocks except to regularly prove the accuracy of your testers.