Newbie: specification of years "today 5-y" works but not "today 10-y"

[loquor]

This could be a newbie issue. Are there restrictions on the years valid in the timescale parameter ? I can get the payload to work with "today 5-y" but not today 10-y". The "all" parameter works "all" - I note that in other parts of the api there are specific limits - are years restricted to 5 or all ? thanks