Chart in sitemap - show more then a year?

According to the documentation for sitemap the possibe syntax for period is:
Valid values are h, 4h, 8h, 12h, D, 2D, 3D, W, 2W, M, 2M, 4M or Y.

RRD4J holds data for 10 years.

Is there a way to display the period of 10 year in sitemap?

At least not a simple one: I tried “period=2Y” (in accordance to 2D, 2W, 2M) and it shows the same result as “period=D”. Seems the documentation is correct and “period=Y” is the longest period that can be presented in a chart.