I an not the Buick expert either. I believe the 14B was the 14 with the gas tank on back deck rather than under the seat, maybe lowered sporty steering column too.
As we know many owners seem to back date their cars, but a car built and sold in the last months of a calendar year and sold as the new next year model are usually called that next year car. A car built October of 2018 as a new 2019 model is a 2019 especially when discussing it over the counter in the parts department.
As far as Bonhams... It often seems that auction house descriptions are bits and pieces taken out of context from the internet and mixed with misinformation from the owner by non-auto employees of the auction house who are trying to fill up the information section.
Does the picture look like an overhead valve engine to you? I think Buick did not use overhead valves on this model because it would have made the engine too wide.