Google Sheets – Using VLOOKUP to Return Values Automatically

Why not have a column that concatenates ACC and UNQ#, like:-

AAA-1000
AAA-1002

Then when AAA was typed in you would get the two options, then you can use SPLIT to get the UNQ# to do the second vlookup.

Assuming the actual finishing date is in Column F and the sheet is called Sheet1, paste the code below inside your spreadsheet under Tools >> Script editor, then hit Save.

/***
* Color Code+ 
* Conditional formatting with cell referencing for Google Spreadsheets
* Support: scripts@bryanp.com
**/

function onEdit() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var s = ss.getSheetByName('Sheet1');
var values1Rule1 = s.getRange('E1:E').getValues();
var values2Rule1 = s.getRange('F1:F').getValues();
var range3Rule1 = s.getRange('E1:E');
var color1 = 'red';

for (var row in values1Rule1) {
for (var col in values1Rule1[row]) {
if (values1Rule1[row][col] == values2Rule1[row][col]) s.getRange(s.getRange('E1').offset(row, col, 1, 1).getA1Notation()).setBackgroundColor(color1);
else s.getRange(s.getRange('E1').offset(row, col, 1, 1).getA1Notation()).setBackgroundColor('white'); }}
};

I used this script generator to make creating the code easier. You can adapt it to your needs.