Water from Melted Ice Sheets dumped into the oceans, early, during the last major warming after the last major ice age. Before, Water from Melted Ice Sheets entered the oceans while Greenland Ice melted and earth warmed more during a major warming and melted more ice and actually raised the oceans to higher levels than we have today. Since the oceans were warmer and higher, it took longer to lower the oceans and more snow fell during the time. The higher and warmer oceans also put more Ocean Effect Snow on land in the South, especially on Antarctica.
The Greenland Ice Core does not go back multiple warm times because it did melt and raise the oceans just like Consensus Climate Science is incorrectly predicting for our future. Look at the previous warm times. If this was going to happen again, it would have gotten warmer ten thousand years ago and then started getting cooler long before now. Look at the steep temperature rise and quick and steep temperature declines that happened before.
I read recently that there is new Greenland ice core data that does go back past the last major ice age, into the ice age before the last one. That data, after it is analyzed and published, will give us snow accumulation rates for more than one full major ice age and for the previous warming to compare with our current warm period, which is very different. This new data is called NEEM and they say they did reach bedrock. This data should improve our understanding of the stable temperature cycle that earth has perfected.