As far as I know, they never shared a slot. But SC Raj was 'extended' to SBC to increase the SBC Raj's frequency to 4 times a week.
Till 1996, SBC Raj was a weekly train, sharing a slot with the TVC Raj (which was an extension of MAS Raj). At this time, SBC Raj was two-day one-night journey departing from SBC at 6:45 in the morning and reaching NZM the next night (and similar timings in the reverse journey).
In 1996, its frequency was increased and a new weekly MAS Raj was...
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started (present day MAS Raj).
In 1997-98, TVC Raj was diverted via Konkan, and I believe this was when SBC Raj's schedule was changed to the present day format, leaving SBC in the night. At this time MAS Raj's frequency was made bi-weekly, and an SC Raj was started, which shared a slot with the MAS Raj.
By 1999, SBC Raj was tri-weekly in more or less its present day timings. MAS Raj was bi-weekly and SC Raj was weekly. Both trains had the same schedule as they do now in the NZM-MAS/SC runs, but the run towards NZM was with different timings. SC Raj used to depart from SC at 7:20PM in the evening, while MAS Raj used to depart from MAS at 12:00PM in the afternoon.
I used to see the SC Raj on PF2/3 while waiting for Gautami to depart from PF1 at SC in those years.
With effect from December 31st 1999, the SC Raj was extended to Bangalore and the SBC Raj's frequency was increased to 4 times a week.
The 2493/94 tri-weekly Raj via Kurnool was introduced in 2010, effectively making SBC Raj a daily train.