I read very few DCs in the 60's, but I did somehow get 3 random issues of ACTION COMICS, each with one half of a SUPERGIRL 2-parter in the back. 2 of these were "part 1", and the 3rd was a "part 2". To this day, I have still never read the other half of any of those stories! But, at least, the "part 2" had such a detailed flashback, I feel as though I didn't miss anything.
The one I had the 2nd half of was "The Kryptonian Killer". What an EPIC! An entire planet of women-- EVIL women-- who brainwash Kara into obeying their orders. My nickname for the story is, "Supergirl Goes BAAAAAAAAAAD!!!" Over the course of the story, she steals, she kills Super-Horse (Krypto flees in terror!), she kills a Phantom Zone prisoner, and then, kills Superman AND commits suicide!! Hard to believe this has a good ending... but the ending WAS very serious and sombre for a 60's DC story.
None of the earlier stories in the 1st SUPERGIRL ARCHIVE book even came close to being that good!
At the time, I was in grammar school. Most guys my age were interested in little league, or joining the Cub Scouts, or (as it was a Cathoic School) becoming an altar boy. My brother did all 3. I was interested in girls. ONE in particular, a really cute girl with big eyes and bright blonde hair. By the 2nd grade, as girls tend to shoot up before boys do, she got several inches taller than me. I was crazy about her. In some ways, she was a dead ringer for Supergirl. Probably why I liked those back-up stories so much.
And yes, DC "Continuity" has become a joke ever since 1986. My best friend many years ago once said to me, "WHY should I care about current continuity if they'll change it again in another 5 years?" I think that was before ZERO HOUR, and we were discussion LEGION OF SUPER-HEROES. So he was proved right. I finally gave up when Mark Waid rebooted history again for what some fans came to call "Waid's World". These days, Paul Levitz is back writing the series again... and I CAN'T bring myself to care. I have a long track record with Tv shows and things where, if I stop watching (or reading), it's almost impossible for me to get myself interested in something again.