Should all Combinations be included in a truth table?
Not as long as the information is unambiguous.

However, in your case, the R0(1) and R0(2) do not matter at all. If you remove them from the table you will get the same formula at the end when working out the table to the formula.

If you would put the entire table, you will also get the same formula. So you just made already some assumptions (for the X). Your table is halfway making the formula already, which is no problem at all. It saves you some time not to put all 16 combinations.

You better can start with the entire table if you cannot trivially make the assumptions you made (e.g. the X-es which can be either 0 or 1).