A vendor who quoted me 'bubble tight shutoff' for several full bore ball valves. No mention even of FCI 70-2 (Classes I thru VI for control valves - some ball valve companies do) or even API 598 on his literature. I looked through all the specs and can't find a definition of the Bubble Tight Shutoff term. I have always crusaded against the term "Bubble tight shutoff". 
A leakrate is completely meaningless unless there is a standard by which it is tested. 
Many specifying engineers think that FCI 70.2 class VI is bubble tight, but there are specific numbers of bubbles allowed and there is a limited size range to which 70.2 Class VI applies. If an engineer specifies he wants class VI on a 10" valve...it's meaningless because 10" valves are not mentioned in that leak class.  
Another confusion is that the standards specify the test conditions, but users expect the valves to meet the same leakage rates installed at completely different pressures and temperatures, and on different fluids.  There is no predictable correlation.   I only would like to add that "Leakage rate factors for Class VI" (see NOTE 2 to Table 3 of IEC 60534-4 and/or Table 2 of FCI-70-2) may be easily extrapolated also over the bigger size (DN 400 = ND 16") mentioned by the standards themselves, as it is clear that they are proportional to the square of the valve nominal diameter...   
In general terms, extending the standards over their scopes and limitations is wrong and leads to contradictions or, at least, unpleasant messy situations... but unluckily it is a common practice among many Customers and Specifiers!!

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