How Hondius bought Mercator's plates
Gerardus Mercator died in 1594 and his atlas appeared the next year, published by his son Rumold. The copperplates stayed with the family until 1604, when they were sold to Jodocus Hondius, an engraver of Flemish origin who had settled in Amsterdam.
Hondius was an experienced engraver and instrument maker, and he knew what he had bought. In 1606 he brought out an expanded edition of the atlas under Mercator's name, with dozens of new maps, many of them engraved by himself. The name Mercator was by then a mark of quality, and it sold the book.
The next generations
After Hondius died in 1612 the business passed to his heirs and then to his son-in-law Jan Jansson, who published the atlas as the Atlas Novus from 1638 and went on to enlarge it into several volumes. The Hondius and Jansson atlases competed with the productions of the Blaeu workshop across the Amsterdam waterfront for decades.
The arrangement was simple: buy the plates, keep the name, add maps. It is much the same logic that publishers still use for reference works.