First:
I think u have configured multiple(more than 1) backup/retention policies for listed VM's, that's why it is showing different restore points.
Please check attached screenshot showing restore points for a VM. I had configured retention policy as 10 days i.e each backup retained for 10 days. So each restore point expiration date and backup date difference is 10 days.
Second:
Yes. selecting X Days option always keep x days worth of backups.
Please check "Table 12-18. Retention Policy Options" of https://pubs.vmware.com/vsphere-60/topic/com.vmware.ICbase/PDF/vmware-data-protection-administration-guide-61.pdf for more details.
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