Presumably, more-recent dates are more accurate, as technology improves with time, often quite rapidly.
The generally accepted date for the end of the Younger Dryas and the start of the Pre-Boreal is 11,500 Before Present calibrated.
The start of the period is relatively sharply defined by a rise of 7 °C in 50 years.
Dates given recently are usually earlier than those given more than 10 years ago.
For example, Iverson (1973) and Rud (1979) give dates of 10,000–9000 BP for the Pre Boreal and 9000–8000 BP for the Boreal, which are uncalibrated C-14 dates based on Scandinavian pollen stratigraphy.
Forest replaced the open lands in Europe, and forest-dwelling animals spread from southern refugia and replaced the ice-age tundra mammals; new climax ecosystems developed.