This happens for two different reasons:
The MLS has some data that is “public” and is for IDX feeds and the public. They also have non-public data that is only available for the realtors to see and search. If the MLS made EVERYTHING public, then nobody would need a real estate agent. 🙂
The second reason could be that IDX Broker has not mapped that field in the data feed because it has been recently added, or for some other reason.
If you want a field that is not in the Datafeed, then we can ask IDX Broker about it. If IDX Broker can’t map this field, you will need to need to write to the MLS and ask them to include that field in the IDX data feed.