Use BigQuery to find the Unity editor versions in use.

unity_product_version_count.bq

SELECT
  line AS version,
  COUNT(*) AS count
FROM
  FLATTEN( (
    SELECT
      SPLIT(REGEXP_EXTRACT(content, r'm_EditorVersion: (.+)'), '\n') AS line,
    FROM (
      SELECT
        id,
        content
      FROM
        [bigquery-public-data:github_repos.sample_contents]
      WHERE
        REGEXP_MATCH(content, r'm_EditorVersion: (.+)')) AS C
    JOIN (
      SELECT
        id
      FROM
        [bigquery-public-data:github_repos.sample_files]
      WHERE
        RIGHT(path, 34) = 'ProjectSettings/ProjectVersion.txt'
      GROUP BY
        id) AS F
    ON
      C.id = F.id), line)
GROUP BY
  version
HAVING
  version IS NOT NULL
ORDER BY
  count DESC

2 notes:

• [sample_contents] has only a sample of all [contents], so you can test your queries on smaller tables.
• identical files are de-duplicated, hence you'll need to account for all copies when counting:

Note for example that id='c4684cd58231b8d76c633a2bc45068594ed3961e' has 549 copies:

  SELECT id, COUNT(*) copies
  FROM [bigquery-public-data:github_repos.files]
  WHERE RIGHT(path, 34) = 'ProjectSettings/ProjectVersion.txt'
  GROUP BY id 
  ORDER BY copies DESC

This is one of those 549 files, all identical:

• https://github.com/0000101010b/GeometricAlgorithms_Unity/blob/master/GeometricAlgorithms/ProjectSettings/ProjectVersion.txt