what does this all imply statistically
From the looks of those charts, the average may be 1.33 but the standard deviation is very broad. In other words, I would not be very comfortable to try to do a model based on this 33% reserves growth factor because there is a lot of variability in this number.
Also, there is no apparent "volume weighting", which would answer the question, is "reserves growth" dependent on field size: do "big fields" tend to be over-or under-estimated to a greater extent than small fields. 100% reserves growth in a big field will cancel out a lot of 2% growth in small fields, even though the average would be 49%.
In any case, this is a central argument in the PO debate, because as we all know, discoveries are about 7 gb per year and consumption is 30 gb per year, so if the reserves do not "grow" by at least 4.25X then only a matter of time before we go into net reserves decline, and ultimately net production decline sometime after that. Also, the 4.25 gets bigger every year as consumption increases.