Connections to the MLS can happen in only one way these days. Looking back it's fun to see the progression through time since the beginning via FTP and SECURELINK.
After a connection is made, there are different theories on how to download the data. This can happen in a few ways.
One way that we connect monitors the data relatively closely. It keeps track of a multitude of items concerning the data. These items would be considered METADATA since it's data about the data.
Recently, on 03-03-15, the METADATA for the BEACHES-MLS/SOUTH-FLORIDA-MLS/REGIONAL-MLS (they are all the same data-wise), changed. Significantly.
In researching why, it was discovered that FLEXMLS, the company that provides the database for the REGIONAL MLS, changed to allow MLS's across the country to provide SOLD DATA to their partners. This is demonstrated by their announcement here:
http://www.flexmls.com/blog/announcing-sold-listings-settings-flexmls-system/
So even though FLEXMLS provides the database for the BOARDS and their members, FLEXMLS does not make all data available to the BOARDS and their members. The change is allowing access to some of the information that previously was inaccessible.
While the article claims that "Consumers get a real-time view of what’s happening in the marketplace and, can make their decisions based on fresh, reliable data from their local Broker and Agent," the reality is much different.
The truth is that the data is only as good as the people that maintain it; the agents and (ultimately) the brokers.
While you won't find any hard documentation, it's been reportedly-known that agents do not mark a property SOLD in the MLS until forced to, despite MLS policy. This force could be by tax records or by broker policy or by a forceful hand from another agent/broker.
The idea is simple. Having a listing as ACTIVE or PENDING or CONTINGENT is free advertising for the agent and pads their number of listings to be higher than it actually is.
For example, if a property is actually SOLD in real life and is marked as PENDING in MLS, two items are happening. The first item is that it shows that the listing agent has an extra property for sale. So while the agent may have 4 listings for sale, on MLS it will show that they have 5.
Secondly, it is both possible and probable that an inquiry could be made on the property. If the interested party is not working with a real estate professional, the following magical words may come from the listing agent's mouth, "I'm sorry that property is unavailable but I have another one just like it."
Ahhh... the magic of real estate.
What's inevitable is that this SOLD data will eventually wind it's way into the wrong hands of which the data is not intended. It's intended for agents and brokers. It reportedly will end up in the hands of Zillow and similar companies who will use it to re-sell back the agents and brokers.
UPDATE: Well that didn't take long. Zillow is moving to get direct access to MLS data. This article from FLEXMLS sums it up:
http://www.flexmls.com/blog/death-by-thousands-of-feeds/
I concur with their attitude towards the move. It is a move that will result in, "no one really knowing where or who is using it [the property data] or for what purpose."
Pretty much game over.
I can hear it now in someone's head, "Why would I get my data directly from MLS when I can get all data from all zombie MLS's from ZILLOW? I'll just combine it with the MLS source when I can and use the ZILLOW source when I can't. No one will ever know. Will they?"
You are correct. No, no one will ever know.