John Buckberrough; our BA authority, has provided a few pages from the BA employee magazine Commentator from October 1950 that explains the design and transition of the old style BA bowtie logo into the newer round one over a period from 1947 to 1950. 
If anyone is interested in offering British American items for sale or trade or simply wants to exchange information or stories about BA - please feel free to contact John.  His email address is This email address is being protected from spambots. You need JavaScript enabled to view it. .  He would be happy to hear from you.