How to deal with unknown values when filtering items

Let's say I have a hotel booking website. Once the user chooses a date and a location the website will list all available hotel rooms in a given area. Each hotel room comes with many attributes, for instance, whether has a pool, offers free wifi, includes a breakfast, whether it requires a deposit and is refundable, etc.

The problem in the real world is that the information about all those different hotels comes from multiple aggregators and "distribution systems" and these often do not provide the same attributes. So it can happen that a hotel has a beautiful pool but it is "distributed" through a system that does not even have a data field for pools. This poses a great problem to the ability to filter results. Of course, the easiest thing to do is to filter only by the information that is available: if we don't know whether a hotel has a pool, don't show it when filtering by pools. But this only works when unknown attributes are rather rare, not when a substantial part of the attributes can be unknow.

Is there a way to show the "unknown/maybe" result? Or is the filtering parading not suitable at all when the uncertainty of available attributes is too high?