(Full disclosure, there was a question on this same topic 2 years ago that went unanswered, but figured I’d give it a try.)
In data returned by the API, there are some fields which don’t appear to be used anymore. Looking at an example player’s /games page, the fields include:
For all 4 fields, the mode value is 0. The average rating is 490 – values appear to be distributed normally around that point. (The mean current Glicko rating is about 1500.)
Are these fields from the system used before Glicko was introduced in 2017?