We got a DAS at DHS for our youngest son last month and it went very smoothly. I prepared a short written summary of needs and relevant accommodations based on his school IEP and evaluation reports from therapists. My parents joined us later in the week, and we knew we would need to get a new card because with them, our party size exceeded 6.
We also had a positive experience with the Epcot guest services. When my parents joined us, we went to Epcot to change the party size on the card. I brought my parents along with me to guest relations while my husband and kids were on Mission Space. For some reason, I thought producing our two extra party members would be sufficient - I can understand why that doesn't necessarily make sense. The Epcot CM advised that they would need to see all seven of us at the same time. So we returned with all seven about 20 minutes later, and the line was quite lengthy at that time. I waited in line and others waited near the benches in guest relations, where our son started exhibiting disability-related behaviors. A CM with an ipad came over to us and was able to reissue the card quickly with a "roll call" of all party members. They were very helpful.
In the end, we never used the card for our party of seven. By the time we used our three FP+ and went to our lunch ADR, he was ready for a break from the park. Point is, I thought the Epcot CMs were appropriately clear regarding the rules and very friendly, understanding and efficient in their implementation.