Hi,

No,
Your profit for the 9 years from Yr 2 to Yr 10 is 149,760 not 91,000. The return is 256%

I think you're mixing up your reasoning and terminology. In 9 years you have returned an overall profit of 256% The 28% you're fixated on is simply the division of that 256% by 9. It doesn't mean that in any year you've returned a margin of ~28% as can be seen from your data.

You can't average averages like you're attempting and draw the sort of wrong conclusions you are coming to.

There is no discrepancy, just a misunderstanding and misinterpretation as to what your numbers are telling you.

Regards