When I was doing the KT Wikipedia seven years ago, I came across this page and used it extensively. It's information that ultimately comes from PlanetGarth.com, a kind of K3P for Garth Brooks. The info is clearly derived from Joel Whitburn's 1999 edition of his top album books, and the years since then with all the rap and Beyonce and Adele million selling things have altered some of the numbers for sure. However, if you scroll down this page -
Summary Of The PlanetGarth Album Stats
you might be as pleased as I was, and surprised at points, to see just how enduring the KT's achievements in sales and charts in the golden years between 1958 and 1961 have been. '61 through '65 paled in comparison but still provided enough oomph to make the Trio #4 on the list of acts with the most weeks with an album charting by decade - for the 1960s, not 1950s. They are behind only Johnny Mathis, Frank Sinatra, and Herb Alpert and ahead of any rock group, including the Beatles and Stones - who sold in their golden years far more singles than albums.
Right above that section on the page you'll see that the Trio appears at positions #3 and #6 for "MOST WEEKS ON CHART IN A YEAR." That 4-albums-a-year contract undoubtedly contributed to this - but someone had to be buying all those albums to put the KT at so lofty a perch. And the best part is - the '60s have been over for nearly 50 years. These stats aren't going to change.
I also enjoyed this one - most weeks with a #1 album in a calendar year:
30, Beatles (1964)
29, Monkees (1967)
29, Fleetwood Mac (1977)
24, Beatles (1965)
24, Bee Gees (1978)
22, Kingston Trio (1960)
22, Prince (1984)
The Trio also places at #12 on the same list with 18 weeks for 1959. The very expansion of the music market with more genres, styles, charts and so on makes me fairly confident that this list is still reasonably accurate, though events like Beatles re-issues, Prince's death, and stuff I just do not get like Jay-z and Kanye may mitigate that.
Anyway, browsing through the linked page is find of fun, at least for a nerd like me.