Search query operators to be used in a api query


I am trying to get a results of the last tweets which have been sent to a a given screenname. in the api it states we can use the operator “TO” in order to search for tweets sent to a user. I would like to know why the query below is no working, Taking into account screen name has been changed to a public screen name. I also would like to know if it is possible for me to get a mentions of a certain screen name and the tweets which they have been mentioned in…

I am using the search query for me to search all of the most recent tweets to an user using the TO:screenname query. How come not all of the most recent tweets come up, which are replies to an original tweet made by the screen name.