“Do schools report data and stats on Spring admits? If not, it seems like a way to increase yield, reduce admission rates and increase average stats.”
Ding ding ding ding.
It isn’t the only reason schools do it, but one reason is to admit kids with lower stats but who get excluded from the USNWR/CDS data (which are based on the incoming freshman cohort each fall).
As the old saying goes, what gets measured gets managed. And spring admit kids, first semester abroad kids are all outside the core incoming fall data set.
Transfer kids are also outside the data set. Check out how at schools like USC and BU the size of the class grows significantly from fall frosh through graduation.