IBES receives data electronically from brokerages on a monthly basis. It is up to the broker to inform IBES (within that monthly "batch file") that the estimates and/or recommendations for a particular company/analyst should be "stopped" (i.e., no further estimates or recommendation will be forthcoming for that company/analyst). If coverage for that particular company or analyst should resume at some point in the future, the data will be included once again in the Detail or Recommendation file.
It could be the case that a broker/analyst decides to stop either the estimates or the recommendations for a company, but not both, but that situation is very rare. Typically, when coverage of a company/analyst is stopped, both the estimates and the recommendations cease.
Coverage of a company/ broker/analyst may be "stopped" for several reasons. For example, if the brokerage has an underwriting relationship with the company. Other causes may be: an analyst quits, and the broker needs time to hire another analyst to cover the company; if a brokerage goes out of business; and if a brokerage is acquired by another brokerage, the data for the acquired broker will be "stopped", while the data for the acquiring company will continue.
Prior to 1993, IBES was not informed by the brokerages if an estimate/recommendation should be "stopped". Looking at the historical data, IBES decided that if the estimates/recommendations for a given broker/analyst/company suddenly disappeared from the database, an entry was made in the Stopped Estimates file on the date of the monthly "run" (data update) by IBES that immediately succeeded the last good estimate/recommendation for that broker/ analyst/company.
IBES manual states that if an estimate is not updated for a total of 180 days, the estimate is stopped. If a recommendation is not updated for a total of 180 days, the recommendation is stopped. (Recommendations are updated by a contributing analyst sending a confirmation, revision or drop in coverage, see more in the IBES manual: https://wrds-web.wharton.upenn.edu/wrds/support/Data/_001Manuals%20and%20Overviews/_003I-B-E-S/index.cfm ).