The RSA came up much later. Udyan used to run merged with the Bombay-Madras Janata express between GTL and CSTM for several years. The Janata was terminated around 1989 and Udyan started running as a full length train after that. For a while it carried 4 coaches as a SBC-SUR slip train. And it was also an SR train with the number 6529/30 (until recently).
The RSA probably came up only recently when Udyan was transferred to CR. Prior to that, Siddheshwar was a CR train with the numbers 1023/24 at first, and then 1423/24 while Udyan was an SR/SWR train.