How can I tell if I used the simplified calculation for the alternative minimum tax foreign tax credit in a previous year?

There isn't anyway you can tell how you answered that question but it may be a safe bet you answered the Simplified Election because Turbo Tax instructs you to use this election because if you used the General Election, you would have needed to adjust your income and deductions for AMT.

if you didn't remember doing this last year, chances are you choose the Simplified Election.