There's a tenant in one of my buildings who's been there less than a year, but somehow he's become my unofficial information desk. 
I needed to get into the utility room and he knew exactly which tenant had the spare key. A delivery wasn't where it was supposed to be and he knew the driver's usual drop-off spot. Then I asked about trash pickup after a holiday and he gave me the answer immediately, including the day it would actually be collected.
I finally asked him how he knows all this and he basically shrugged. 
He's not employed by the building and doesn't have any responsibility for this stuff.  He's just apparently been paying attention to everything since he moved in.
Honestly, every building seems to have one person like this, and I'm starting to appreciate having one around 😂