I think that the second table in your example is confusing and the first one is wrong.

The clue is to look at what voltage you read from the chart for a temperature difference of zero, because the answer has to be zero volts. In the second chart there are two rows for 0 °C; the first row has 0 V at the right-hand end, but the second row shows 0 V at the left-hand end. Therefore the first '0 °C' row must show values for temperature differences from -10 to 0 °C, and the second row for temperature differences from 0 to +10 °C. In between the two '0 °C' rows there should be a new set of column headings reading 0 1 2 3 etc. That would show you that the correct voltage for a +20 °C difference between two type J thermocouple junctions is 1.019 mV.

Your first table seems to be copied from the second one, but without the negative temperature rows, so its column headings are simply wrong for the positive temperature rows that are shown.

I think that the second table in your example is confusing and the first one is wrong.

The clue is to look at what voltage you read from the chart for a temperature difference of zero, because the answer has to be zero volts. In the second chart there are two rows for 0 °C; the first row has 0 V at the right-hand end and negative voltages in the preceding columns, but the second row shows 0 V at the left-hand end followed by positive voltages in the subsequent columns. Therefore the first '0 °C' row must show values for temperature differences from -10 to 0 °C, and the second row for temperature differences from 0 to +10 °C. In between the two '0 °C' rows there should be a new set of column headings reading 0 1 2 3 etc. That would show you that the correct voltage for a +20 °C difference between two type J thermocouple junctions, when the reference junction is at 0 °C, is 1.019 mV.

Your first table seems to be copied from the second one, but without the negative temperature rows, so its column headings are simply wrong for the positive temperature rows that are shown.