By using various tram and German railway websites, I have managed to trace the former identities of the OTP stock previous at Croydon tramlink. All five vehicles were built for German Railways (DB).
The two Type Klv53 railcars are:
058 - ex. DB 53.0692-3, Sollinger Hutte #7808, 1978 (now at Crich)
059 - ex. DB 53.0551-1, Robel #54,13-5RW82, 1975 (now at Rushden)
The three Type Kla03 trailers are:
060 - ex. DB 03.0594-6, FX Kogel #41-01514, 1975 (now at Rushden)
061 - ex. DB 03.0621-7, FX Kogel #41-01541, 1975 (now at Crich)
062 - ex. DB 03.0819-7, AW Bremen #194, 1979 (now at Rushden)
The three trailers are currently missing from the preserved section, so perhaps it could be updated to include them?
I hope this is of interest to someone!