With this poster, go ahead and fill in the missing edges at upper right corner and lower right, please.

On this one, I am a bit confused as it is already mounted.  I see there was paper loss at the upper right corner and a bit of loss on the lower right corner.  Maybe there is even some loss on the left edge, but I did not look.  I assumed that paper filling on the corner should have happened before the poster was mounted, right?