Some of the real estate agencies have their own codes in their ads, even for houses that aren't their own listings. This forces potential buyers to contact the agency that ran the ad rather than going to someone else with the MLS number in hand. Their will also be an MLS number for the property, unless it is exclusive to that agency. Even then it may have an MLS number.

That may be what you are seeing.

Most agencies can't put their own office numbers on listings in the MLS. What you are seeing online is being fed from the MLS directly. What you are probably seeing is listings from two different MLS's. In my area, there are four MLS's (Four counties all within 1/2 hour of each other) because of this, each county has their own MLS. Some agents choose to enter the listing in more than one MLS system, depending on the location of the home. This is why you will see different formats and sometimes the same listing with two different numbers.