For the holders of 1/1 medals in Counter-Strike.

What is a 1/1 medal? Only one legitimate player holding that specific medal.

This does not mean "very rare". Major winners, for example, are not 1/1. The winning team receives the same Champion Trophy Medal, making it a 1/5.

Apart from Service Medals, a Map Contributor Coin can be a 1/1 medal, if the map only had one contributor.
There are almost no 1/1 medals in Counter-Strike, despite it being the most popular shooter game of all time.

Service Medal Summary:

2015: No 1/1 medal, as Tier 2 was the highest and has 1,500 holders.
2016: Tier 4, 440 players. No tier 5, or Tier 6.
2017: Rosco & lemonMONSTA - Tier 5 (Pink) BOTH BANNED
2018: Rosco - Tier 6 (Red) BANNED
2019: Johnny - Tier 5 (Pink) Note: Scan Lab BANNED

From 2020 onwards, due to the prevalence of boosting, many people hold the highest tier medals and they are no longer 1/1.
In fact, a 1/1 medal is becoming rarer and rarer, and it is likely Counter-Strike will never see another 1/1 medal again.