1. There is no limitation on the free offer of the Gospel. All who believe will be saved.
2. There is a limitation of the efficacious impact of the atonement. Only those who believe will be saved.
3. What realization did Calvin arrive at? Do you have documentation of this, or is this something that someone posted on a website, but you haven't taken the time to verify? (Or, more probably, it is a misunderstanding from one who doesn't know the distinction between the Gospel offer and the atonement any better than you seem to demonstrate.)
Of course. I wholeheartedly agree with you on this.
But Jesus' death was "for the sins of the whole world." The atonement was sufficient to the point that even if EVERYONE believed the blood would cover all.
The gospel is REALLY offered to all. It isn't just "pretending" in its offer. That would make God duplicitous.