file:Dropdown lists

You should first ensure that the numbers entered in column H of each sheet is formatted as numbers and not text

Then you can use formula:

=SUMIF(INDIRECT("'Mr X Issue "&B$1&"'!$D$6:$D$18"),$A2,INDIRECT("'Mr X Issue "&B$1&"'!$H$6:H$18")) in B2 and copied down and across the table.

Sample shows som REF errors, because those referenced sheets not in your sample