You can estimate the date of the outbreak's origin with phylodynamics, using the diversity of circulating SARS-CoV-2 and its mutation rate to estimate the time to most recent common ancestor (TMRCA) as 27.11.2019 [CI 07.11.2019 - 11.12.2019]. "Considerably earlier" doesn't fit the evidence
It's possible that a mutation emerged in november 2019 that pushed the R number up. A "mild" form of the virus could very easily have lingered in China/SEA for years.
https://virological.org/t/update-2-evolutionary-epidemiologi...