I will soon update, this is just the theory part to my reply
Your guesswork does not obey the mathematical distribution models that I firmly believe it should obey. This flaw is apparently because you did not use equilength (in log scale) brackets.
The distribution of bitcoins should, in my understanding, conform to one of these distributions, where X=log(number of bitcoins) and Y=(number of owners of the given number of bitcoins).
Now, if we calculate the integral over a bracket (which is one unit-length of the X-axis), we find the total number of bitcoins held by people in that bracket.
From the mathematical, probabilistic nature of the distributions, follows that the total bitcoins owned by people in different brackets cannot behave arbitrarily. Ie. the parameters are:
-how many bitcoins do the top owner(s) have
-how many owners are there in total
-one or two parameters to define the shape of the curve.
This can easily be checked by arranging the data to log-equilength brackets and demanding that the number of bitcoins owned by people in the bracket is either continuously higher than in previous bracket, or lower. At most the 1st derivative should have 1 root and behave nicely.