I really enjoyed looking at this. There are so many beautiful visuals that take me back to my childhood. All of that late Modernist cutting and hot glue...

Too bad there isn't any commentary in the article. The "how" from the title is completely missing. I can summarize but I'll miss a lot:

1) The laser printer did not arrive until 1985. It was the killer app for the one-year-old Macintosh, along with the introduction of desktop publishing and photo manipulation programs. Being able to use a computer for graphics work was a HUGE CHANGE: the cost of getting pre-print ready dropped by two zeroes. A set of workstations and the normal-paper printer for them was way more than the cost of light tables and wax heaters, but it was also within an office budget instead of a factory floor.

2) The Internet. Suddenly you didn't care about Pantone, CMYK, or whether the ad was going to be printed at all.

Heck, and I'm only getting into the tech of it. The changes at advertising agencies, the rise of women in business, the virtual office letting more people freelance...