I think I have just answered my own question, because I have noticed the picture of set 130 in Fareham station in 1953 on the 'Blood and Custard' website, and the suffix 's' is there. along with notes on the absence of First Class '1's on the composite. Most useful site, and I should have checked there first! https://www.bloodandcustard.com/SR-CoachingSets-LSWR-CrossCountrySets130-324.html