I have seen Charlie Chan movies appear online, then disappear. No doubt, you were fortunate to see "Mr. Moto's Gamble" before it eventually gets removed. That film is definitely NOT in the public domain.
As I thought. I was surprised to see Lon Chaney junior in the movie as a thug named Joey, though. His presence in MR. MOTO'S GAMBLE really made my week. Mr. Chaney went on to portray the three movie monsters - Frankenstein's Creature, the Wolf Man, and Dracula.
Thank you for including "Mr. Moto's Gamble" in the Chan film line-up. Given its evolution, it is most appropriate to join Lee Chan in a Mr. Moto mystery.
It was nice to hear the referances to Charlie too.