Were K's just made in Constantinople during the 60's while the Avedis were made in the US? Is that the difference? From what I've read, Zildjian was effectively 2 companies for a number of years until the end of the 60's when it split into Zildjian and Sabian.
K's (during the 40s 50s 60s and 70s-until the last (Turkish made) 1978- were made in Istanbul, Turkey. The Constantinople name change (of the city) was__1930. The stamp on the cymbal changed to Made in Turkey, Istanbul 1940 or so. Prior (the K. Constantinople) said Made in Turkey, Constantinople
So, American Zildjian started in 1929 (to present)
Turkish Zildjian began in Turkey 1623 (to 1978).
So from a period of 1929 until 1978---there existed two - separate - Zildjians running concurrent - from two different continents (Turkey and the United States.) there was concurrent competition, litigious.. competition.
I'm in Jeannette, Pa. If you ever want to talk cymbals Or USA Gretsch I have both..
here a good story:
https://www.company-histories.com/Avedis-Zildjian-Co-Company-History.html
here's a good story II:
http://www.turkishculture.org/music/musical-instruments/turkish-cymbal-285.htm
And here's a simple site:
http://robscott.net/cymbals/
And be aware the origin of all the metal insignia, "stamp" names, stamp ID, dating, was done by a fellow member here
Name: Drumaholic---Bill H.
http://vintagedrumforum.com/member.php?u=3487