The SSN puzzles me. In 23 years...I have never asked for a SSN while taking a routine complaint. If the contact results in arrest...detention officers at the jail will obtain a SSN. So...the reason the officers in question asked for the SSN is pretty simple: Someone above their paygrade told them to.
When you are making a public contact with a complaintant or a subject...you must get all pertinent information...and that includes contact information. All the information regarding the incident also comes at this time, so it can go into the report.
You have NO idea the amount of paper we have to generate for those above us! Even when we get a 911 call from someone who's "neighbor was rude" or my personal favorite "he said the f-word"...we have to write a report. There is information that is expected to be in every report...and if it isn't there...guess what rolls down hill.
All i's must be dotted and all t's must be crossed. From our shift commanders to prosecutors...(professional nitpickers) they want this info and we HAVE to get it. Some departments have personel (not sworn) who's sole job is to enter stats from contact cards into a gee-whizz computer program to show data on call volume/response time ~ type of incident/versus geographical area...it goes on and on and on.
They also want us to account for all the time we don't spend wolfing down donuts, free coffee, and stomping on your civil rights. Because you know...that's what we do according to some folks.
Think of it this way....You're a plumber. Someone calls you to plunge their toilet. When you get there...they say..."No, it's cool, I found my plunger" A lot of calls, even through the 911 system are "plugged up toilet" calls. The fact is SOMEONE made that call, and like a good plumber (but with faster response time)...we have to show up to make sure the turds are gone.
Taken another step...we wouldn't even BE talking to you if YOU hadn't called. YOU, apparently, wanted to talk to a cop. So, we showed up.
You might not believe this...but not everyone who makes the initial complaint is always the true victim. There is such as thing as the "race to the phone"....the kid on the playground who starts a fight, gets his clock cleaned, then runs to the teacher to rat out the kid who he picked on, but got his butt whupped. The interview phase is where we often figure this out. The way that is done, is to get ALL the information possible.
Everyon has a boss...and typically every boss in a department above the rank of patrol sergeant is a tactical desk operator...and have a lot in common with a diaper...always on your butt and usually full of crap.