How to make a range for tail rows on a categorized table in Numbers with JXA scripts?

Question

I hava a simple table like the following in a Numbers document and i want to select the last row(s) of the table with JXA script.

I can use the following code to make a range on the last row(s) of the table and select it.

tbl = Numbers.documents[docName].sheets[shtName].tables['demo'];
tbl.selectionRange = tbl.ranges['4:5']; //select last two rows
tbl.selectionRange = tbl.ranges['5:5']; //select the last row

It works. But when i enabled category on column DATE of the table, the above code will select another row(s), not the last.

I know the actual number of rows changed to 7 in this case, because when the category was enabled, two new group summary rows raised. But i don't think i should modify the code for making range. Actually if i changed the last line of above code to tbl.selectionRange = tbl.ranges['6:6'] it will throw error:The range value cannot be retrieved. (-10000) It seems like the maximum value of row for ranges cannot exceeds the maximum value of the row number indicator. I can select the last row by using codetbl.selectionRange = tbl.rows[6]; but this approach only selects a single row. How to select or make a range for multiple continuous rows in this scenario?