Information would pass between neighboring tribes over time. Even if a small region had gone centuries without fire, the knowledge could return. Indeed, fire it

Information would pass between neighboring tribes over time. Even if a small region had gone centuries without fire, the knowledge could return. Indeed, fire itself could be transported between tribes if one lost theirs. For a continent-scale loss of knowledge, you'd need a continent-scale loss of fire lasting generations. Any event that could cause this would certainly have left clear traces.