All right, I might as well take a stab at this....
Belthasar foreshadows that the party will have to climb Death Peak in 2300 A.D. Yet, how does Belthasar know he's going to die at the Ocean Palace?
Well, if you consider that Janus already knew about this beforehand, then therein lies a possible answer. Think about it, it sounds kind of extreme to pretend that a little boy (no older than 4 years old) could predict right then and there that Crono would perish shortly (and I am of the idea that he actually knew for a fact it would be Crono and when he who would die, but refused to tell the party so as no to be discredited by them for the 'ramblings' of a crazy child).
If you are of the idea that Janus' black wind abilities are innate than this could work out for it:
Maybe Janus had already forseen this would happen through the interpretation of the Black Wind beforhand, and told Belthasar all about him and how he was going to die.
Rather maybe he was the one who taught him how to be sensible and be able to percieve and listen to the Black Wind's howls and as such, he already knew he would die as soon as he heard about it (in the Black Wind).
If this is true, perhaps Belthasar's own abilites exceed Janus' and he is able to tell not only when and who is close to death, but how it will happen.
Normally, I'd consider this some kind of huge oversight, like the fact that Yuji Horii wrote the concept of the Time Egg long before Masato Kato actually made 12000 B.C.
Wow, I would
really like to know 'exactly' what it was that Kato rewrote into Hori's already made up script.
That would clear up SO many things for us. Especially for us fans who regard Chrono Cross as the better game in the series.
Anyway, the use of the Time Egg servers no other purpose than to revive Crono. It's tenuous as a result to ascribe this to the Entity's planning or Belthasar's awareness of its actions. What do you think?
I think this could
almost constitute yet another plot hole that could be added to CT's already identified ones. Probably the reason it's not listed there would be because of the fact that it's an incomplete plot hole. It is something that was simply left unexplained due to the fact, as you mention, that it was probably an oversight over the writers' different styles making up the game's plot.