You seem to assume that the interest rate has decreased in a straight line over 5 years, by 0.081%. If the interest rate had been higher in that time, more interest would have accrued, thus increasing the amount owed/left to be paid.
Looking back over the loan when 1 month euribor went up the interest part of the repayment increased to reflect this.
I'm looking at the two monthly repayment amounts used below in isolation and knowing the rate has fluctuated over the period am asking, if the interest rate now is lower than it was in March 2003 and the capital amount outstanding is also less now how is it that the monthly repayment could be higher? Has the lender made a mistake or am I wrong in my calculations?