LOL, it was enough of a mess to begin with, but it seems KMDB has updated both Jang Cheol pages and made things even more confusing
What's causing the most trouble here, is that the Lee Jae-yeong that is Unknown Korean Actor (3) is given the stage name of Jang Cheol according to the KMDB. Since they interviewed him I assume it's correct, but of all the films I could confirm he is in, he's never been credited as Jang Cheol.
I have a theory that maybe he got it on the set of North Shaolin & South Shaolin as both Lee Jae-yeong's feature in it, but this is just a hunch. And good luck thinking the Hanja credits might help, as I went through them and it's mostly gibberish.
The Unknown Korean Actor's will be one of my first ports of call. My magic will be swift and terrible.
Cheers