I can offer you is sympathy but wish I could do more as what you are describing is not like any GD conditon I have heard of I wish there was a hospital dedicated to skin diseases like MD Anderson in Huston. You have to keep trying and another biopsy could help. From my experience biopsies have to be taken at the right stage of a breakout. My GD biopsy was negative. I was almost at the end of my initial GD breakout which lasted 1 year about 5 years ago when I went to a new derm who took one look and listened to my symptoms and immediately told me I had GD. Others treated it like my Allergic Contact Dermatitis, so of course nothing helped previously because basically no meds help with GD. Yet when she took a biopsy it came back negative. She told me at the time of the biopsy that for the GD biopsy to identify GD it needed to be in the active stage. Yes I had the clusters of classic rashes all over front and back torso, upper and lower but they were scabbing at the time of biopsy. All I can think of is for them to accurately find the GD it has to be a fresh active area. Also what is your biopsy testing for? Is it limiting the test to GD? Can they biopsy for hives, shingles or other skin conditions with the same biopsy. You could have multiple skin diseases and your doctors are limiting their ideas to GD.
You are one to study. Have you gone to the New Zealand Derm site, dermnetnz.org, a site which helped me identify one of my 3 forms (once again incorrectly treated as my original form of eczema by derms. Start with a blank slate and search their skin site for your symptoms, not assuming it is GD. This site has the best batch of photos of actual patients with the skin condition. You will find various appearances with each type, even GD as we know has variations, but if you search though the pages you may find a photo of hive like rashes like yours.
I though my GD might be coming back as my lower back in the center was itching, yet confused because upon closer inspection the itchy area was just one wildly itchy non healing bump! Nothing remarkable in appearance but it would not heal for at least 3 months. I could scratch of the scab once crusted to only have it return and never heal. It never had puss and didn't bleed but a bit, like you mentioned. My back in that area is still not smooth as I can feel a few little bumps, but they do not itch. I believe GD permanently has changed my skin layers. This one bump was so itchy it felt like if was dozens of GD papuales. I changed my gardening clothes from loose 100% cotton jeans, held up with a 100% leather belt (I'm not allergic to the 100% or the leather) to 100% cotton bib overalls. The belt and the jeans but pressure right at this bump and rubbed it when bending over. The overalls have zero pressure. I also broke down and used a steroid on the papuale. Steroids never helped with GD. Yet after eliminating pressure and adding a steroid after 2 weeks it was 60% better. Stopped steroid and still better, but scab is still there and will leave it alone this time. I think the friction irritated my GD damaged skin and this papuale may not be GD but simply weak skin. Now just minor non-troubling itch, yet it's not gone. I still make my cilantro smoothie and plan to for life. Still this doesn't account for your random hives, mine seems to be triggered by pressure and it was not a hive.
Your situation really sounds like an allergy the way it moves around in areas not normally associated with GD. Does it happen more if you go outside? I have a friend my age that just this year started getting hive like welts on her arms, legs, scalp, face and even unexposed areas after she gardens. It sure seems like allergies, but when she gardens she never leaves her patio or sidewalk, just reaching into flower pots or little flower beds. No dietary changes. Maybe it's in the air as she lives in a wooded area.
You helped so many of us with your input about cilantro and hope others on this site have ideas for you.