I don't know how hard it would be to make the dialogues more detailed, but when I played Cross those days, I found some funny things:
I took Zappa to Dead sea and he was surprised when he saw Karsh and the dragoons frozen in time, so he knew his son had already "dead".
When I visited Zappa's house later, he talks nothing about that, but only metioned to call him when need.
It seems Zappa didn't tell anything about the fate of the dragoons to Zippa, so she still asked Serge to find Karsh.
So I put Karsh and Zappa in team and talked to Zippa, she only said "Oh you bring Karsh back" or something like that.
Then I kicked Zappa out of the team and put Viper in.
This, Zippa, Zappa and Karsh did had a long talk, but it seemed Zappa/Zippa still didn't know what happened in the dead sea, and they asked about other dragoons' fate...oh my, Viper was right there you know...
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Well, even if you brought Viper, talked to Zappa, and Viper took him Karsh's alive. Zippa still said the same thing, sigh...she must be deaf and blind.
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It seems they didn't know Riddel at all...