I think WEG may have gotten their ship sizes mixed up (e.g. a Star Destroyer probably isn't 1,600 meters long), but they did make some good products, especially in the early days.

Though my thought is based around the actual set size of the movies, and the fact that I doubt that they were getting too much specificity from Lucasfilm about the details of stuff.

Yeah, little pro tip: many star wars sizes are wrong.

In some cases its simply that the model makers of the original movies weren't concerned with it (like the size of the neb-b). In some cases its a matter of EU writers listing a scale in feet, and editors changing it to meters, but not actually converting the numbers (several of the vehicles in WEG sourcebooks). In some cases it simply a matter of an author pulling close enough numbers out of his butt and never expecting anyone to challenge it.(the AT-TE)

The Imperial Star Destroyer ended up at 1,600m because the model builders for Star Wars wanted it to look BIG, but only had the rough guideline to "make it look a mile long." 1 mile = 5280 feet = 1,600m.

It's only as things evolved did more specific measurements come into play. The folks at WEG were simply working a best guess...