Again from endometriosis.org:
Before the introduction of laparoscopy in the 1970s, endometriosis could only be diagnosed during a laparotomy, major surgery involving a 10–15 cm incision into the abdomen.
I put this here because while it’s often noted that endo seems to have a familial link, there may well be reasons why other family members might not have been (or might not currently be) diagnosed. Currently — yes, even with laparoscopy no longer being a new thing — being diagnosed with endo can be quite a significant investment of time, money, convincing, frustration, pain, etc. For previous generations of family members, this may have been even more true.