Perhaps that gave existing Britannia jockeys a taste of the -300
In BAL the -200 and -300 fleets were operated by different crews. There was a detailed examination of whether to fly both, but the decision was no. One of the factors was that the Boeing manuals for the 2 variants had totally different layouts, and info was difficult to cross- reference. I think this was a legacy of BAL being a very early 737-200 customer.