PTO handles basic calculations for F.1116 without problems.  What PTO doesn't do and won't even give you any prompt or diagnostic for is where various adjustments are required by the Code and regulations.

If your "unused" means carryover from prior years that were not carried back, yes, they get applied to the current year when you have excess limitation and the carried forward amount is shown on page 2 of F.1116 regardless of whether it can be utilized.

If the foreign tax available for credit from the current year after applicable scaledown is larger than the limitation, the excess credit may then be carried back/forward.

With each F.1116, PTO generates a Statement that breaks down FTC carried forward from each of the last 10 years and how much of that is utilized to support the amount reported on page 2.  There is also another version of that in the Workpaper which breaks down the amount of credit available for carryback and carryforward.