I live very near Mason Hallow Nursery (
http://www.masonhollow.com/ ). They specialize in Hostas and offer something around 700 varieties at any given time, so when I say I've seen 'dozens' like it it may be an exaggeration, or an under-exaggeration, but I know I've seen more than a couple apple green, yellow/golden/cream edged hostas there.
We know we can eliminate anything registered or not offered before the approximate time it was purchased though, so that should help knock a few right off the list of any possibilities. If it could only be remember what company it was bought through, it would be much easier to find out what they offered in that time frame and compare.