Upgrading system

[Nozomi]

0-1=100%
1-2=100%
2-3=93%
3-4=86%
4-5=79%
5-6=72%
6-7=65%
7-8=58%
8-9=51%
9-10=40%
10-11=31%
11-12=22%
12-13=13%
13-14=8%
14-15=2%

these are straight from item.enc files that manages the upgrading system. so these values are true.

no way these are right.
Did you ever try upgrading with safes? With those rates you'd need an average of 50 safes just to upgrade from +14 to +15, which is usually not the case.
(please fix my math if it's wrong).
As far as I've noticed by means of empirical methods (aka upgrading 6-7 pieces myself to +15 with safe and enhancers) the rates from +10 to +15 seems to be the same, with an average success rate of 50%.