No idea on dates or whether this will help narrow things down but as I am going from memory alone here...

The Solars on the 93/94 were originally at Chester (displaced Prestiges from 21 series) prior to the move to Sunderland Road and subsequent repaints.

The four acquired Solars at Deptford (branded for 20/20a), were if I remember the correct order: Chester (often on 721), Washington (x3/x4), Sunderland Road (51/52), then I am not sure whether it was the 9 or x36/37 which came first, eventually ending up on the 20's