I think two art notes is fine if they are necessary, it's notes dictating artistic direction that are to be avoided, and if an editor thought this particular story needed an author note, you could always just have it ready. Are you submitting this to the editor you met at a conference? If so, I'd include the author note. If you are submitting to agents, maybe just keep it ready and if there is interest you can let them know the ed's suggestion and that you have one and go from there. People get a little crazy sometimes about art notes and berate authors for using them, but if they are necessary to understand the ms, then they should be included. I know of authors on these boards who have been asked for them by editors because the story needed clarification. Two is not too many.