It was not uncommon for some Eagle artists to change their art as they worked on it and some would go to the the length of painting new sections, cutting them out and gluing them onto the original board to cover the sections that they were not pleased with. There are many examples of Dan Dare art boards with entire panels replaced in this way.
Cutaway artist Leslie Ashwell-Wood also used the method. In fact his Gannet anti-submarine aircraft cutaway in Eagle Vol 3 Number 44 has almost the entire sky and a good section of the sea replaced in such a way. At least a third of the art is a separate section glued down onto the original board. Unfortunately this is not the kind of information that is contained in The Eagle Annual Of The Cutaways which is a pity because the art used in the book does show an example of this occurring.
On pages 62 and 63 the book reprints Ashwell-Wood's painting of a Thornycroft 31 foot cabin cruiser crewed by a family of four in which the father relaxes at the stern of the boat overseeing his son's steering of it. This illustration is one of the eighteen that the book also reproduces at the front and back from the original art boards. The original art board of this cutaway shows the figure of the father incomplete and presumably the final version of the figure was an additional piece glued down to the board which has since separated again.
One of the more juvenile sections of the book is the "Men Of The Cutaways" section where the author invites the read to identify which cutaway a dozen or so male figures came from including the cabin cruiser father. What a pity the pages couldn't have been used instead for the rather more informative purpose of showing us differences between the original art boards and the final printed version.
The Eagle Annual Of The Cutaways is available from Amazon UK.
There is no readily available listing of all the cutaways in Eagle but this website by Wake Carter lists almost half of them and the issues of the comic that they were in.