With some older tyres, this is OK. There are layers of cord at shallow levels which are designed to be worn away. these tend to be high pressure tyres which older Russian types tend to have. As long as the wear indicator groove is visible, there's life left.
The british V bombers used to have the same sort of tyres. When we landed our Victors anywhere other than home we usually got the comment 'Have you seen the state of your tyres?" The Victor's tyre pressure was 325psi, a lot higher than modern airliners.