My understanding is that no, they aren't.. as there are now fungi that can break down lignin, and so coal isn't ever going to be formed in those quantities ever again, no matter how long you wait.
Coal contains very little lignin. Coal is still being formed in bogs, or anywhere acidic and anaerobic.
Anaerobic fermentation is still used to stabilize harvested bamboo. Bamboo stem contains sugar making it susceptible to termites and rot. Bury it in riverbed mud, bacteria will quickly break down the sugar before the lignin and cellulose, then you pull them ashore and wash mud off to stop the reaction.
Before this fungus came along, trees would fall over, and just pile up, every forest was a vast carbon sink, no matter how soggy the ground was. That's where our fossil fuels came from.
Good point! The carboniferous era must have been a hell of a time, wish I could have seen it.
A Billion years is a long time , who knows what will have evolved by then