When you copy value from Result grid, data will be retrieved as per your Query options setting in SSMS ( Query -> Query Options -> Results -> Grid -> Max characters retrieved)
Default characters value is 65535 and data copied from result grid is only of length 65535
If you want to increase maximum number of character just increase this value (for example you can add a Zero after last number..)
AX / Dynamics 365 For Finance and Operations blog 
