>Try

>=INDIRECT("'" & INDIRECT(LEFT(ADDRESS(1, COLUMN(),4,TRUE),1) & "7") & "'!D" & ROW())
>

>>For your information, CELL("cell") does not bring information from the current cell if the second parameter is omitted, but from the last cell that was changed.
>>
>>From Help:
>>CELL(info_type,reference)
>>Reference is the cell that you want information about. If omitted, information specified in info_type is returned for the last cell that was changed.
>>
>>I'll take this as homework and will report back :) Thanks again.

Because the worksheets went into columns with two letter names I had to adjust for column name length.
$A$4 contains the name of the source column, because each worksheet gets its data from a different column.
$A$5 contains the value to show if a sheet does not exist ( default is = NA() )
This is not optimal for recalculation speed, but good to save developer time :)

=IF(ISERROR( INDIRECT("'" & INDIRECT(LEFT(ADDRESS(1, COLUMN(),4,TRUE),LEN(ADDRESS(1, COLUMN(),4,TRUE))-1) & "7") & "'!" & $A$4 & ROW() )), $A$5, INDIRECT("'" & INDIRECT(LEFT(ADDRESS(1, COLUMN(),4,TRUE),LEN(ADDRESS(1, COLUMN(),4,TRUE))-1) & "7") & "'!" & $A$4 & ROW() ) )