Want a named list with non-continuous cells - excel

Question

I thought this should be a common thing but my search has not returned anything meaningful. I'd prefer an Excel solution, rather than VBA.
I have a proposal sheet with details like number (col D), date etc and a column saying if the proposal got converted (to business).
On the invoice sheet, I have a list of invoices. The requirement is to always refer the proposal number against which this invoice is being raised. For removing human error, the applicable proposal numbers should be available as a drop down. Hence the drop down should only show the proposal numbers against which the invoice can be issued (proposal got converted to business).
This means that non-continuous cells (say, D3, D4, D6, and D10 - where proposal converted is 'yes') from the proposal sheet should be the values available in drop down of data validation in the invoice sheet. How do I achieve this?
Edit:
Adding an image that is representative of the 2 sheets.

Answer 1

My solution involves creating a list using the INDEX MATCH or INDEX SMALL method to pull multiple results from the data that can be used for the dropdown.
I added a couple of extra columns to count the number of times an invoice has been invoiced and then a further Yes/No to make the index formula easier to follow. You'll see that my example only has 2 values to select from as the others have been fully invoiced.
The scary formula in Q1
=IFERROR(INDEX($A$2:$H$1000,SMALL(IF(($H$2:$H$1000="Yes"),ROW($A$2:$H$1000)-1),ROW(1:1)),1),"")
This is an array formula so you must use SHIFTCTRLENTER instead of just ENTER in the formula bar. {} backets will be added if you do it right.
To break it down, INDEX($A$2:$H$1000 is selecting your proposal data and some more rows below (1000). SMALL(IF(($H$2:$H$1000="Yes") is looking at my extra Yes/No column for "Yes". ROW($A$2:$H$1000)-1) is returning the row number minus 1 to account for the fact that our range starts at A2. ROW(1:1) is saying that we want first match in the list and the ),1) returns the vlue in the first column of the range $A$2:$H$1000.
Because ROW(1:1) returns the first result, you will need to autofill down in order to pull more results. As you do this the formula will copy down as 1:1, 2:2, 3:3...ect. I filled down to row 50 to allow for a decent amount of results.
You could set your validation range to Q1:Q50 but then you would have lots of empty space in your dropdown so, have a look at cell R1.
="Q1:Q" & COUNTA(Q1:Q50)-COUNTBLANK(Q1:Q50)
This formula creates a range based on the results in column Q. You can use that value in the data validation range by entering.
=INDIRECT($R$1)
Thus creating the dynamic range that you require.
You don't have to use the extra columns that I added but the formulas are;
=COUNTIF(M2:M1000,A2) to count the number invoiced
=IF(AND(F2="Yes",G2<E2),"Yes","No") to check if it can still be invoiced.
if you do want to use them then I'd recommend formatting your data as a table so that the formulas are copied down automatically on new rows.
Also I'd advise putting the index list on a different sheet so that rows are not deletes etc.