Dynamic ComboBox used as index into variable length list

I have a worksheet that contains tabular data. Column A contains an ID# for each row. There can be multiple rows with the same ID# so what I want to do (on a different sheet) is have a combo box whose input range is dynamically updated to include a list of numbers from 1 to the number of entries in the tabular data that have an ID# matching a particular cell's value.

So, for instance, assume the tabular data is on SheetA, and the combo box and cell with the value to match are on SheetB.
If the value to be matched is 1200, and SheetA has six rows with the ID# 1200, I want the combo box to list six entries; 1, 2, 3, 4, 5, 6.
If the value matches only two rows, the combo box would list two entries; 1, 2.

That way, I can use the combo box's cell link value to populate SheetB fields from the nth SheetA row, as selected by the combo box (This part I think I know how to do)

Thanks for the quick response MarvinP!

Unfortunately the dependent dropdown solution doesn't work since it deals with populating the combo box with values from a range rather than a sequential index into the matching rows in the range.

The advanced filter also doesn't quite get me there either since I only want one of the total rows in SheetA with the matching ID#, not all of them.

I'll try to obfuscate my data and attach a sample.

I've attached a sample workbook with dummy data.

If you look on the Risk tab, column P contains the combo box in question. Based on the risk number selected in A1, I want the "Select Mitigation Step" combo box to have a list of numbers representing the individual mitigation steps, from the "Mitigations" tab, that have an ID number in column A matching the selected risk.

So if Risk tab cell A1 contains '1', the Select Mitigation Step combo box will have the numbers 1 through 8, because the Mitigations tab lists 8 steps associated with risk 1.

If Risk tab cell A1 contains '2', the combo box would only have 1 through 4 in its list because there are only 4 mitigation steps associated with risk 2.

Once I can get the combo box populating properly I can use the selected number from the combo box to populate the Current Value fields (1-14) in the Mitigation Step Update Table by pulling the appropriate data from the Mitigations tab.