Blackstone has been very good about retesting if I have a question. You need to ask them within a week or two because they hold the samples for a couple of weeks then recycle them. They are also very willing to answer questions. I think the bottom line is that Terry is more knowledgeable and his premium service covers some data that Blackstone doesn't test for. For example his lab measures fuel dilution directly rather than estimating based on flashpoint. My understanding is that many engines on newer cars have a moderate fuel dilution problem, particularly if driven short trips in colder weather. The only way to know for sure is to test and this is particularly important if one is considering an extended oci.