Tooltip with most recent date

I built a YOY line graph with three years of data on it. I have data points for almost every day. The chart is using a calendar week number field from a calendar/date dimension table as its x-axis. I'm having trouble using any date field as the tooltip though. The goal is that when hovering over a set of points, it shows the most recent date in that area instead of just the week number (I've done this with other charts, but data is only from one day a week in those). Any suggestions on how to achieve what I'm looking to do? Image is included.