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Can someone explain to me the difference between these two talkgroups? Would listening to only one or the other be a bad idea (e.g. missed radio traffic)?

Disp 7B (TGID 5008)
Disp Simulcast (TGID 4688)

I'd like to set up a scanner locked-in on San Diego FD dispatch.

Does one start before the other? (and yes, every second counts)
Does one pick up better throughout the county in general than the other?
Does one carry more radio traffic than the other?
Does one transmit special data ("tone outs"??) and the other doesnt?

I don't understand the difference.