From the search API response, the client (UI) can easily tell if the API has returned the exact number of entities that matched the search results, or it retuned an approximation, and there could be more entities.
If the UI specifies limit as 10, and numCursors as 10, the maximum possible entities returned would be 100. If the number of entities in the response (identified by total) is less than 100, then it is guaranteed that an exact number of entities have been returned. There is no approximation here, and a + should not be shown next to the total number of results. If however the API returns 100 results, there is a chance that there may be more results, so the UI should add a +.