They picked it up in mid-2020 from Northern Star - the resource...

They picked it up in mid-2020 from Northern Star - the resource was already largely there. Check out the announcement from the time (June 2020) on the KZR website.

From an article at the time of the original transaction in 2020:

"The 217sq km project currently holds a JORC Code (2012) resource estimate of 20.8 million tonnes at 2.5 grams per tonne gold for a contained 1.65 million ounces. The project has already produced 350,000oz of gold."

"Kalamazoo will pay Northern Star up to $17.25 million deferred cash consideration. This payment is contingent on 250,000t of ore being minedand 250,000oz of gold produced. There is also a 0.75% royalty payable to Northern Star on any subsequent gold being produced. Similar royalty structures will apply to other metals produced on the tenements."

From memory, Kalamazoo's update to the JORC lifted the indicated grade but reduced the overall ounces (could be wrong there). So yes, picked it up for free and the resource was already there.

Note that all of the payment conditions with respect to NST have been passed onto DEG as per page 2 of the option agreement release "On exercising the Option and acquiring the AGP, De Grey will assume all of Kalamazoo’s deferred consideration and royalty obligations in respect to the AGP".