Multiple times this happened to me. I cast [[Repeated Reverberation]] and then [[Sundering Stroke]]. If I choose two targets, all copies will have to choose two targets. That´s fair and within the rules, learned that the hard way. But then after I knew I the creature was dying, I want to assign only 1 damage to the creature and the rest to the player, and it won´t let me. On the last time it happened I had to do 4 to the player and 3 to the already dying creature, or vice-versa, with both copied spells. Is that because on the original spell I chose 3 on the player and 4 on the creature?

edit - RIP cardname is wrong and cant edit the title lol

2nd edit - thanks for the replies and I would also like to say another thing I learned the hard way: copied spells don´t have adamant...