Hello, Cronos - maybe one way to look at this is that Heaven is populated by those who are God and those who are not. It would not sound unreasonable to me that only those who are God would know who the elect are. So, God would naturally rejoice at the salvation of all the elect, even though He already knew it in advance. To all others, it would be news and so there would also be rejoicing.
I do not understand your statement that if there is an elect, there are no sinners. All of the elect were and are sinners. The elect have simply been purchased, bought and paid for, and forgiven. We are wholly owned within the family of God. The sins Christ died for include all sins of the elect, past and future.
The Scriptures tell us that Christ died for the sin of ALL men, not just the elect...Thus, all men are redeemed. But if all men are redeemed, why are all men not saved?
Regards