Que: Eduard Masks: two sets of masks or one for each coat?

I got some Eduard Masks to use with my Revell Mig-21 F-13 thinking it will be worth a try to see how much time they save. There are two sets of masks in the packet and the instructions suggest that one is for the inside color and one for the outside color. Now they appear to be the same size and the instructions indicate that they both go on the outside of the canopy; one coat of the inside color and then a coat of the outside color on top. This is all well and good considering I want to display the canopy closed, but it begs the question as to why two sets of masks. In the past, I have painted both colors one right over the other without removing the mask. Does Eduard suggest removal and reapplication because of some problem with removing the mask with two coats of paint on it? It seems to be twice the effort for the same effect if I were to remove one and then reapply a second mask for the second color. Not to mention that the chances are increased for not aligning the second mask just right and getting some inside color showing through or vice versa. Any thoughts?