Ok, so I guess I better explain how this works.
When you use a calculator the optimal way to get results is to enter the values before you do anything to get a starting range. This range will usually be fairly wide but the important thing to know is that no matter what, the values of your actual pokemon will not get better or worse than this unless there's a fault with the calculator or you entered something wrong, no matter how much you upgrade it.
Once you've done this you then write the values down somewhere so you don't lose them, punch in the new values after you evolve or power up your pokemon ONCE (no more or it won't work) and then click the 'refine' button. What this does is looks at the new possiblities and discards any that weren't in the original batch because ultimatley this is a process of elimination. You continue this process until there's only one possibility, you're happy enough with the ones in the range you have or you've decided that the possibilities in the range are so abysmal you've kind of given up
What I suspect you've done is you've clicked on 'find IVs' on each entry which means it's treating it as a brand new monster each time which means it has less data to go on than if you'd refined it. I'm afraid it's highly unlikely that your venusaur has IVs better than 20% based on what you started with :/
edit: Looking at the possibilities I think you're likely stuck at 9%, but I'm basing that off the fact that almost all starter line pokemon found in the wild usually have one of their IVs set to zero.