Depends, you can try and find companies in different business sectors and fill in gaps for each (with permission of course). The company pays with their list (and a fee to you?) which another could use. As long as it doesn't affect their competitive advantage, it could be a freeish way to grow the list. Not every scenario but there could be a niche, especially if you were the middle man and masked where the data was from and where it was going.

But by the same token, they are something that is worth keeping up woth the joneses on. so this might be a case where equilibrium farms out the low hanging fruit and the proprietary differentiation is on the harder/rain-maker parts of the list. Just seeing the glass half full, in other wrds.

Unless it's a complementary product.