Okay, in even simpler terms : All-Time Great is a fighter who retired and is still worth talking about - and will always be worth talking about - simply because of how good they were at boxing and/or how much they achieved.
As far as I know, none of these guys are in. Chucho Castillo Santos Laciar Jiro Watanabe Gilberto Roman Ernesto Marcel Jose Medel Lionel Rose Rafael Herrera
All good fighters... but I'm not sure, I'd call them ATGs. Going by achievement, I guess a case could be made for Laciar. And maybe for Rose, for being the first aboriginal champion. Jose Medel was a fine fighter in a stacked bantamweight era - but I don't see, how he classifies as an ATG.
It depends, how low you want to set the bar. Personally, I think "ATG" is a label that should be reserved for VERY special fighters... and not those who were just very good.
Marcel should be a shoe in for a top 10 FW, and is a lock for top twenty. Rose, Castillo and Herrera are all close, or in, the top ten at BW. They're all-time greats.
All Time Great? Can't put my finger on any one thing. You just know it when you say their name. For example, when I blurt out Dana Rosenblatt!! Real loud did your mind go to All Time Great? Mike McCallum! Eh...nope. if you have to think about it doesn't qualify. Hector Camacho! Nope, coulda don't count. Joe Louis! The system works
Dubblechin's post is correct. "ALL TIME GREAT" is obviously a designation that is valid for .... well, ALL TIME. No one gets thrown off the list when a new one is added.