Why is version of a package on index.golang.org very different from the version on GitGub?

This query:

wget “https://index.golang.org/index?limit=1&since=2021-05-28T01:21:42.994935Z

returns this record:

{"Path":"github.com/concourse/concourse","Version":"v1.6.1-0.20210527214455-4a0d7de97e1a","Timestamp":"2021-05-28T01:21:42.994935Z"}

However, https://github.com/concourse/concourse/tags shows that the last version is v7.3.1.

How can it be that these versions are so different? Where does the version v1.6.1 come from?

It looks like you’re limiting to one record. Maybe there’s more than 1 version since the date in the query string and maybe one of those includes version 7.3.1.