Job postings are updated on a daily basis.
Profiles data are sourced from vendors and updated quarterly. Every quarter, Lightcast receives new and updated profiles information from vendors and incorporates these profiles into Lightcast's profiles dataset. You can get news about profiles updates on the Profiles Changelog.
Job postings and profile data both make use of various taggers, machine-learning tools used to "tag" information on a posting or profile. These taggers include the skills tagger, company tagger, and job title tagger, among others. These taggers are human-curated and are constantly being improved through research and through feedback provided by users. Updated versions of the taggers are released every two weeks.
When this happens, all job postings and profiles are re-run through the taggers. This can result in counts for various aspects of postings or profiles changing. In other words, the same report, run before and after a tagger update, could produce different skill, company, title counts, etc., since the taggers were improved.
The Profiles Changelogs linked above also include information about tagger updates, as well as links to visit the changelogs of various taggers to see what changes and improvements were made to the taggers themselves.