Not every site on the web promotion no deposit casinos are good. Some have information the is not up to date and the promotions have expired. Others just find offers and put on their site where they are exclusively for certain sites. This means they are not going to give you the promotion and since you already have sign up, you can not go back and claim it from a different site. How to avoid falling into this trap is when you see an offer on a site and you go from that site to the casino you should see the no deposit bonus. It might be located on the promotions page or it will be directly on the page you first landed on. If it is a coupon code promotion either they have provided you with the coupon or again you will see it on the landing page.
There is good sites which has exclusive deals, please beware that these exclusives are normally meant for computer users not people accessing by mobile. This does limit the amount of bonuses you can get if you only play on mobile casinos as well as some of them do not even have a mobile version of their casino site. You may have experienced this already and I am sure the day will come when it all changes but for now this is just the way it will be. No deposit bonuses may be a thing of the past in the future as well, as the casinos really do not like offering but at this point they still must since many give out these credits still. If there is only a couple left in the next few years I can see this ending for all casinos, so now is the time to collect as many as you can.