Central line specials

In the thread on coronavirus, the service on the Central Line seem very similar to the off-peak service I recall when I used it to travel to school in the late 60s/early 70s. This thought led me on to the Specials that were run for my school. I went to St. Clement Danes in Du Cane Road. As the school had a tie with St. Clement Danes Church in The Strand, every year the whole school travelled from White City to Holborn by a Special, and returned by two specials. In my naivety, I thought that special trains were scheduled, but I now suspect that the trip to Holborn was just a normal eastbound service which was effectively reserved as far as Holborn, and I suspect that the westbound trains were probably trains that started from Liverpool Street, or others that were tipped out at Liverpool Street. I can't now remember whether the westbound trains actually terminated at White City, or whether they carried on. What I do remember is that, for obvious reasons we ran non-stop to Holborn and on return.