Some retailers are able to ship out a day before embargo, counting on the shipping itself to deliver the new product on the day of launch. Canon Rumors reports it has gotten reports indicating some are receiving shipping messages for the RF 16mm f/2.8 and the RF 100-400 f/5.6-8.
Both lenses were announced at the same time (oddly) as the Canon R3, the sports camera that presumably would be fitted to L glass rather than these more affordable lens lineup fillers.