The NPV formula assumes a cashflow at the beginning of the period, (unlike the PV where you can specify the start or end), hence you need to add the first value of 950 to the NPV for the subsequent 35 periods.

As per your statement above, you mean, by adding the first installment to the NPV of 35 installments gives you the NPV of the Payment at End of the Period,

If am wrong please correct me...

regards
sing_ideas