Yup, just as I remembered.........
In order to successfully merge all the parts, a newer part 1 is needed. Every once in awhile they are on
ebay - either as a whole or one or more of the four parts.
If you have the money to spend, I would buy a new Part 1. I've given it some thought, but the idea of moving all those stamps is a bit too much. Sooo, I will do my best to be content with the separate Parts.............