I have allergies to all seafood and spinach (and kiwi fruit but only that grown in California - not a problem that comes up too often).
The first thing that I noticed was that I booked several ADRs for dinner and noted the seafood allergies. Then a few weeks later I booked ADRs for some breakfasts. Since I knew what I was going to order (had eaten there before), I didn't note the seafood allergy. Apparently, that doesn't matter because when we got to Kouzzina for breakfast, the chef came out and talked to me. I told him that I'd already planned to order the stacked breakfast and that I'd had it before (sweet potato hash with two poached eggs, artichoke spread and olive bread). The potatoes are deep fried and he told me that they would cook them in oil that had never had any seafood cooked in it and which was regularly filtered.
When we went to Jiko's the chef again came out and talked to me. I ordered the barbarie duck breast (recommended by him - that's the other advantage of talking to the chef) that came with a side of potato with spinach. He was originally going to make it without the spinach but then came back and said that it really needed greens in it to be true to the dish so substituted arugula for me. I doubt I would have ever known the difference. Delicious (spicy, but wonderfully aromatic and flavourful).
Victoria & Albert customizes the menu for you and will take out the seafood course and substitute with something else. If the amuse bouche has seafood, they will make something completely different.
At Teppan Edo, they did an additional pre-cleaning of the grill and made my steak first because some others had ordered seafood.
We're heading back in a couple of weeks and I'll be going to the same restaurants as well as a few more (mostly ones we've been to before).
(Side note: we followed up our last visit to WDW with a B2B
Disney cruise. I also didn't mention the seafood allergy on that since we'd cruised with them before and I knew that I could mention it the first night. However, the first night when I ordered the server mentioned that one of the appetizers I'd ordered had anchovies in it. I hadn't even said anything about allergies and it didn't occur to me until the next night that I hadn't but that they already knew. Either they already had it on file from previous cruises or it carried over from my WDW ADRs.
On a second side note: on our June
DCL cruise, I was warned about a particular appetizer which had something, don't recall what, as an ingredient which was pre-packaged. Because they cannot guarantee that pre-packed items unless otherwise noted have not come in contact with potential allergens, they will always warn you).