Wandsworth Common, Streatham Common, Norbury, Thornton Heath, Selhurst, Purley Oaks, Purley and Horley clearly have the same architectural hand; unsurprisingly given they were built as the LBSC Railway quadrupled from Clapham Junction to Balcombe Tunnel Junction. East Croydon was, but the station’s had a significant rebuilt since. I assume Coulsdon North was as well.
No idea why South Croydon didn’t get the same treatment. I’ve a vague recollection that St Leonard’s Warrior Square is in the same style.