Blanket Purchase Agreement Start and End Dates in OTBI

Summary:

Looking for table that provides the same start/end dates as the Manage Agreements screen's in application

Content (please ensure you mask any confidential information):

Through some Googling and searching through the community, I've found that the code below pulls the purchase orders where the PO is on a PO Line that was created from a BPA. I was concerned that the start_date and end_date fields in the PO_HEADERS_ALL table were related to the PO and not necessarily the BPA, but I was surprised to find that these 2 fields are blank. What am I doing wrong and where should I be looking for the Blanket Purchase Agreement start/end dates?