I was diagnosed during a lap. I think they do need to go internal to diagnose. I think pain and location of pain varies widely in endo. I had almost zero period pain. Just the odd month or during a miscarriage. I did though, tend to occasionaly get pain on urination or a BM. The BM pain was very sharp and I would almost pass out at times. I never thought I had endo, as I did not have period pain.
I had surgery for what they thought was a pos appendicitis , I had gone in with extreme pain from what I thought was a pos burst cyst.
I was home alone. I think I went into shock, as I could not stop shaking and was freezing. Then I passed out. After waking in a few hours, I called my partner. Went to the hospital. Turns out it was a burst cyst and I had extensive endo. My uterus was covered on the outside, and as said half of one ovary was removed. Apparently, the endo affected my bladder and I was told 'it is in the wrong place'. Where that place is, I do not know but it explains the pain I sometimes get. My intestines were covered as well. All that and I never knew. I should say though, a few months before the surgery, I had begun to have pain around O time, which I had not before. I think must have been from the endometrial cyst.
I think if you look up endo pain, you will get as many variations as people. Also as said, endo has stages but I have learned the stages do not necessarily correlate with the amount of pain.