Also keep in mind, reasonable suspicion as judged by the courts is based on what the officer knew at the time of the stop. My computer has a box that tells me that the complainant left their contact information. At the time of the stop, I believe that the caller has left his name and phone number. If it later turns out that he lied, that does not diminish my reasonable suspicion, because
at the time of the stop I believe my caller was not anonymous.
1) Whether the information was provided to the police in a face to face interaction, allowing an officer to directly assess credibility;
You are correct, almost never the case in a 911 call
2) Whether the informant can be held responsible if her allegations were untrue;
As stated, if the call is anonymous, this does not apply. If the caller leaves any name and contact info, it is assumed to be true.
3) Whether the information would not be available to the ordinary observer;
The ordinary observer does not notice things like license plate numbers as they drive around the city during their average day. If someone takes the time to tell 911 a license plate, it is presumed they had a reason to focus on it.
Heck, ordinary observes seem to know little more about cars than how many doors they have and what color they are. I constantly take reports from witnesses who can only say "it was a green sedan."
Therefore, if specific detail is given, such as make, model, license plate, or even a bumper sticker, this is all considered information that an ordinary observer would not know. It generally implies someone who was involved in the incident.
Again, they may be lying, but the officer must go with the information provided. More credence is given to greater detail.
4) Whether the informant has recently witnessed the criminal activity at issue; and
Self explanatory.
5) Whether the informant’s information accurately depicts future activity.
In other words, if they say he was last seen heading west on main street, and the cop sees a matching car 10 blocks west of the crime on main street, that adds credibility to the original 911 call.
The totality of all of these taken together may create enough reasonable suspicion to initiate a stop. All points need not be met. An anonymous caller who gives excellent detail may be good enough. A person who gives their contact info but only a vague car description may be enough.
The question can't really be answered here, because there is no hard and fast line. Lawyers argue these points on cases all the time, and sometimes evidence gets tossed out because the initial stop was deemed to not have enough RS. Sometimes people end up in jail because they were driving a similar car in the wrong place at the wrong time and they had meth on them, and the courts found that there was enough RS for the stop
even though the person driving that broke absolutely no law that caused the stop.