I just want to add that the grid both on the server side and on the client-side (CSOM) keeps record only of the rows / columns that are currently visible and available (current page) - this is done for optimization purposes - the grid will be very slow, if not impossible to work with, if it stores all data and information about potentially thousands of rows, while displaying only one Page of 20 rows.

So, if you to obtain a reference to a row that is not on the current page, then I am afraid this is not possible using the grid API (you will need to either explicitly page to the page needed or query your datasource directly).