Mosaic Trisomy 18 - Time to Change the Definition

When a medical definition does not reflect reality, which needs to change - the definition or the reality? Definitions directly impact the actions of  medical providers and their patients. Take for example, this definition of Mosaic Trisomy 18 by the nhs.uk
 "... such as mosaic or partial trisomy 18, do survive beyond a year and, very rarely, into early adulthood. But they are likely to have severe physical and mental disabilities."
Is this true? No! There are a number of successful individuals with Mosaic Trisomy 18 or 13 who were not even diagnosed until adulthood. Unfortunately, because of this definition, parents are given a very bleak outlook with a strong recommendation of abortion, or refused medical services. 
It is true that depending on the organs affected, some individuals will be more severely impacted, but often this is  the only narrative that is shared. Can a woman make an informed decision when accurate information is withheld?

Do you think that it is time to change the definition that "we very rarely" make it to adulthood and are "very severely physically and mentally" challenged? I would love to hear your thoughts.