Data Validation, with some options allowing or restricting custom values?

[mcarterlgk]

I am trying to build an interactive form in excel. I have most items working as I need, but have come upon an issue that has me stumped.

I have a list of structures (Column D) with a series of columns next to it. Each column is representative of one of the options for that structure. Not all columns apply to each structure and some structures allow custom values in addition to the choices available in the columns.

I need a cell (A6 in the table below) to return a drop-down list of only the options that pertain to the structure contained in A3, and to allow a custom value based on the "Custom Allowed" Column E.

[TABLE="class: grid, width: 868"]
<colgroup><col><col><col><col span="2"><col><col span="6"></colgroup><tbody>[TR]
[TD][/TD]
[TD]A[/TD]
[TD]B[/TD]
[TD]C[/TD]
[TD]D[/TD]
[TD="colspan: 6"]E F G H I J [/TD]
[/TR]
[TR]
[TD] 1
[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD="colspan: 6"]Spacing[/TD]
[/TR]
[TR]
[TD] 2[/TD]
[TD]Structure[/TD]
[TD][/TD]
[TD][/TD]
[TD]Structure[/TD]
[TD]Custom Allowed[/TD]
[TD]2'[/TD]
[TD]3'[/TD]
[TD]4'[/TD]
[TD]5'[/TD]
[TD]6'[/TD]
[/TR]
[TR]
[TD] 3[/TD]
[TD](Validated List)[/TD]
[TD][/TD]
[TD][/TD]
[TD]A[/TD]
[TD]Yes[/TD]
[TD]2'[/TD]
[TD]3'[/TD]
[TD] [/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[TR]
[TD] 4[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD]B[/TD]
[TD]No[/TD]
[TD]2'[/TD]
[TD]3'[/TD]
[TD]4'[/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[TR]
[TD] 5[/TD]
[TD]Spacing Options[/TD]
[TD][/TD]
[TD][/TD]
[TD]B[/TD]
[TD]Yes[/TD]
[TD]2'[/TD]
[TD]3'[/TD]
[TD]4'[/TD]
[TD]5'[/TD]
[TD] [/TD]
[/TR]
[TR]
[TD] 6[/TD]
[TD](List Needed)[/TD]
[TD][/TD]
[TD][/TD]
[TD]D[/TD]
[TD]No[/TD]
[TD] [/TD]
[TD]3'[/TD]
[TD]4'[/TD]
[TD]5'[/TD]
[TD]6'[/TD]
[/TR]
</tbody>[/TABLE]


So Structure "A" in A3 would make A6 return a list of (2', 3') and would allow custom values.
Structure "B" in A3 would make A6 return a list of (2', 3', 4') and would not allow custom values. etc, etc.

I don not want the empty options to show up as spaces in the drop down list, so I will need a way to eliminate empty options in the list too.


Summary

I would like to have A6 return a list of available options for the structure A3 in and only the options, not a fleet of empty options from empty cells included in the validation row. Based on the value in column E i would like to be able to allow A6 to accept or not accept custom entries.

Not sure if I am even phrasing this correctly, but any input would be greatly appreciated.