If you are modelling glazing using an entry from the glass library then you do indeed have to also enter a frame width and frame conduction. The glass library parameters are only for the glass portion of the window, not the frame. If your overall U-value is not as expected, I would first check your frame conduction value. Also note that the spreadsheet showing a U-value is for a standard window size. Larger windows will have proportionally less edge and frame effect so lower U-value. Smaller windows have higher U-values due to dominating edge and frame impact.
Conversely, if you use the simplified method for glass type definition then you enter the whole assembly U-value (NFRC u-value) including the frame and then set your frame width to 0.
The advantage of using the glass library is that the solar impact at different sun angles is more correct as there is a curve for solar as a function of sun angle.
