never let a sample sit that long off hand all I can think is TBN may drop as weak acids work on it. Also some "gunk" may settle but I would think that this lab would thoughly mix the sample. Any others I missed?
When we do water based machine coolant samples they must be tested within a few days or the bacteria present will grow FAST and mess up the test results. Not a problem is a PCMO sample.
bruce