While changing my bike chain, I noticed letters stamped on some of the links. The old chain (Shimano CN-HG53) has »OG« stamped on some links, while the new one (Shimano CN-HG93) has »RL«. Google doesn't find anything useful. Anyone knows what it means?
The RL and OG might be date codes. Assuming these are 2 different chains, RL would denote 1993-December and and OG would denote 1990-July. If you think they are newer than that, the chart isn't up to date, but if you follow the pattern, RL could be 2019-December and OG could be 2016-July. The second set of dates makes a lot more sense based on what I can see visually from picture.