My husband had a similarly difficult time remembering phone numbers and exact addresses for some past jobs, especially since he's been self employed a lot. As mentioned, just fill out as much as you know. I think they're looking at the big picture, not nitpicking over these smaller details.
Just an update, we had our vacation in the states. We went through immigration in Seattle and I asked a person where we should go since my SO is on a tourist visa and we are just visiting. We were directed to the non citizen line. Everything went smoothly and we had a great time.