My read is the same as yours. Looks like Anadarko has sold Chief its lease interest outside existing units. Do you think this is the case with all Bradford county units? I see from the doc you posted that is is at least across several townships.
About 890 for March, 660 for April and so far 215 for May have been filed. I haven't seen any in Litchfield twp. where Anadarko is not a partner and not counting leases in which acreage is fully contained in a unit, I would think that would about cover the entire county. And they apparently aren't finished yet.