It's in general a bad idea to rely on TWOV on seperate tickets. Airlines dont have to obliged to give you clearance to make the transit.

Airlines get fined if anyone decides to throw away the other ticket and, say, claim asylum or try enter the said country, so without a through ticket they do have the right to deny boarding. Just like we cant use seperate tickets to interline for many airlines now and you cant force them to do so.