There has been some discussion about how to know in advance whether a hotel does or does not have a Concierge Lounge. I did a random search of hotels throughout the world, added one I knew did not have a concierge lounge, and found the information in the section "About this hotel" - then "About this property". There it tells you if and how many concierge levels there are at a given hotel. So it's not on the main hotel page but if you click over you'll find it. That, of course, does not ensure that it's open 7 days a week, but usually there's compensation (such as coupons, breakfast in the restaurant, etc.) if it's not.
I guess there must be some inconsistencies, because I'm remembering that one Insider was writing that there was no CL, even though there was a Concierge Floor in the hotel. I wasn't happy to hear that because that has been my barometer: I go to the "Printable Fact Sheet" area of the hotel's website, and there it will list how many Concierge Floors the full-service property has. As I say, this has always been my barometer, and if I see a Concierge Floor (or Floors) listed, I always assume that there is a Concierge Lounge as well. This has worked for me 100% of the time (at hotels, not resorts).
For a handy brand directory which you can download and keep on your laptop/notebook for easy reference when you're on the road and you do not necessarily have internet connectivity: Marriott Brand Directories