derszoger –
The Gemara in Avodah Zarah 9a says the world will last 6000 years. It is unreliable for two reasons: 1) It is technically unreliable because there are other dates recorded in the same context that didn’t work out exactly the way they were predicted. 2) We generally cannot take any of these kind of Aggados literally, or even guess what they mean until after they happen, especially ones which deal with mashiach and end-of-the-world scenarios. This is a concept made very clear by many of the meforshim (Rambam, Ramban, et al).