Hi,
I wanted to get some clarification on interest rate swaps valuation.
My understanding is the following:

If valuing on a reset date, then we can simply apply the formula:
(Current fixed periodical rate  Inception fixed periodical rate) * Notional * Sum of PV factors 
However, if valuation point is NOT reset date, then the preceding formula doesn’t seem to work. What is the underlying logic of why it doesn’t work in nonreset dates?
For nonreset date, I apply = coupon * (sum of PV factors) + notional * last PV factor