NBC buries the lede - Steele started working for FBI in Feb 2016
https://www.nbcnews.com/news/amp/ncna897506
The records also indicate that in February 2016 the FBI “admonished” Steele. A federal law enforcement official explains that an admonishment is typically given when a person begins a stint as a confidential informant and annually thereafter. It is a briefing on the rules of being an informant to ensure the source complies with guidelines set by the Attorney General, and usually not criticism of the source.