Yang Taiji was created by Yang Lu Chan (1799–1872) after he spent time in Chen village learning Chen Taijiquan. Due to historical and political reasons he changed what he had learned when called on to teach publicly. In private he, his family and his ‘indoor’ disciples continued to practice Chen Taijiquan.
My first confirmation with this came when I traveled to San Francisco in the 70s to study with the famous Tai Chi Master Kuo Lien Ying. He was not available but a friend and I spent a week working with his wife, Madame Kuo, a former Buddhist nun and Taiji master.
I had some familiarity with Taiji by that time and was surprised that what she taught us was essentially Chen Taiji.
Yang Lu Chan had two sons: Yang Ban Hou who’s lineage Kuo followed, and Yang Jian Hou who’s lineage led to Yang Cheng Fu. The Yang Ban Hou lineage was oriented to Chen Tai Chi, the Yang Jian Hou lineage more to what we know today as Yang Tai Chi.