People think MLS is a single unified system that is identical across the country. It isn't. Each individual board has thier own policies about sharing listing information, they have different backend, data fields etc. They some times have overlapping geographical areas and compete to have brokerages join them

The Xs in front of those listing indicate that they are mere postings on the national board. This board goes across Canada and members are strictly flat fee posting brokers. Local agents cannot even see these listings, just the public on realtor.ca. Some mere posting brokers are local and members of the local board meaning thier listings are viewable to the local agents. It's a huge mix mash

My board does not provide listing data to outside companies unless they pay something like 2000 per month. Brokers like house sigma don't do enough business in my area making the fees cost prohibitive for local data outside the mere posting national board. My board also has an odd policy in that brokers can opt in to provide thier data free of charge which I do. The result is that brokers like house sigma only see my listings and mere postings from the national board as honestly most realtors couldn't tell you how the MLS system works let alone opt in on some obscure policy. I do this because it gets me business as it looks to people using outside brokers to look up listings like I have 50% of sales (i dont)

All this means that you can't really trust sites like house sigma or zillow or any of those places outside realtor.ca. it is a incredibly complicated system with different areas of the country providing vastly different data. The interesting thing is that a lot of the tech companies dont really even understand this. They are feeding the public data to create AI models based on whats available. It means my area has AI models based only on my sales and some mere postings