In apartment listings, what is a Referral-ID?

I’m curious since I just signed a lease a few days (approval pending until landlord comes in on Monday) for an apartment through one realtor and he told me he took it off the market. However, on craigslist, I’m still seeing other real estate agencies advertising the apartment I signed for. Even though the pictures are slightly different (from other similar units in the building), I’m sure it’s the apartment I signed for, unless the landlord managed to have several similar units free for October 1st- in which case, I’m going to be very paranoid that perhaps there is some secret infestation that happens at night that I don’t know about. The referral ids for many of the listings are also different. Are referral ids referring to the ID of the apartment unit?