I guess you could say they added on, but to me i always saw it as changing things to fit things to the new story they wanted to tell. In s1 they wanted O/L to be this big romance. Oliver was in love with Laurel (in the writers own weird demented way), her picture was "important" to him, he wanted to be with her. S2 happens they change it to gear more towards Sara and s3 it was as if nothing had happened, now they are adding a new epic love romance to the flashbacks to help parallel Olicity.