First, last summer Vermont legalized the use of OA/GLY pads. Recently the USFDA has withdrawn the use. So be it. Anyway...
I used OA/GLY pads last summer. I did see some control on varroa population growth. I think it most useful in conjunction with other treatments.
I added pads in early May. At that time I noted two colonies with serious young mite populations in the drone brood. Surely a dead colony in August.
Checking those two colonies in July the brood was healthy, no noticeable IBS, and nice pearly white larvae. I think the pads should be replaced after a couple months once they are propolized. I would still use your post harvest treatment.