More or less.
It was famous a game lost by Cho Chikun in the #50 Oza (2002), against O Meien. 2nd game of the match, both players in byo-yomi, Cho ahead and fully concentrated, didn't realize that O had already played and after the countdown, he lost. Very shocking, can't even hold his tears. In the end, he lost the match 3-2.
A second case happened in the #14 Hiroshima Alluminum Cup (2019). Nakamura Sumire vs. Hane Ayaka. Players must hit the clock. Already in yose, Ayaka forgets to hit the clock. Sumire knows, and when she plays, she pushes the button (that was already down). Some people say that Sumire looks at it, hinting "push your button". Again, countdown and Ayaka loses on time. She doesn't understand what happened, another pro tells her (not the referee, there is no referee) and she accepts the mistake and the loss. 2 rookie players that perhaps don't know very well what to do.
But recently, in this era of youtube, I saw another game. #77 Honinbo prelims. Kobayashi Koichi vs. Cho U. Also, no referee, only recordkeeper, and the players must hit the clock. Again in yose, Kobayashi forgets to hit it and Cho inmediatly points to it. The game goes on, Cho wins and all is fine.
Nobody wants to win like this. I can understand that it's up to the player how to use your time, and it's your responsability to play when you have to. Even more in a big game. I don't really know the protocol, if Sumire could say something or not. But Cho and Kobayashi, more veteran players, do whatever they want to. Who is going to complain? And, btw... Kobayashi is Cho's father in-law