Roy Bacon (who compiled the list) obviously used the 'new model' release dates for the 850s as he'd have been working from the factory records (now held by the VMCC) which apparently has little or no information on 850 models as the NOC records "become non-existent after mid-'72" as I was informed some years ago by the NOC.
For instance, Roadster/Interstate/Hi-Rider 850 (Mk1) date of "3/73" is obviously new model release as it was reported in the weekly motorcycle press during March 1973.
AN records (which Roy Bacon probably would not have been aware of) show 850 (Mk1) production commenced during January 1973. Unfortunately, there is also a large gap in the AN records between 305549 and 317848.