This sounds like the "Ships in: xxx yyyy days " notifications on various Apple web stores. It is a pretty poor predicative indicator these days. Typically it is only highly accurate when people look backwards in the aftermath of a refresh.
Apple spends $100's of thousands (if not millions) on infrastructure to allow them to keep a limited amount of inventory on stock and in the pipeline. Sometimes a small bubble may pop up where some unexpected folks decide to order and Apple runs slightly short. That's not sign of a refresh.
A relatively low number of folks buy 12 cores. The inventory for those is going to be the thinnest and most susceptible to minor bumps in demand.