James, they are all the same action Sir. Some vendors just list the DA/SA, SA/DA arbitrarily. They are all Double Action 1st trigger pull and Single Action after.

Regardless of terminology, a PPK is Double Action if first shot is fired by using the trigger with the hammer down.
Single Action after first shot, because hammer will now be in the cocked position.
You can fire the first round by cocking the hammer first, and that would be Single Action and of course Single Action for all the remaining rounds until the mag is empty.

AC/DC in guns all the same.

the two are interchangeable and mean the same thing

It’s the same thing.