All 12AX7's have an amplification factor (µ) of 100 ("high-mu"). Ideally, every 12AX7 should yield the same gain when placed in the same circuit; however, in reality there are comparative gain differences among 12AX7's.
This graph is based on the average gain and noise measured from different tube brands, using the same number of samples for each brand. It should not be assumed that every single 12AX7 from a specific brand will match its place on this graph. The gain rating is only a relative reference (e.g. a rating of "10" does not mean ten times louder than a "1").