Any way to separately Validate and create a Dropdowns in Google Sheets?

Question

Sample Scenario:

Sheet 1 has a 3 Dropdowns from sheet 2
Sheet 2 has two lists, {"A";"B"}, and a second dynamic list that copies the first IF the value doesn't already appear on sheet 1

The behaviour I'm looking for is to validate on list one, but provide the drop down from list 2.

Current Problem:

if a user selects "A" from the dropdown on sheet 1 (pulling from the dynamic second list on sheet 2), it will no longer show up as a selectable option in the further dropdowns (as intended), however the first drop down now shows as invalid (because that item is no longer on the dynamic second list)

Alternately, if I use the first list, selecting an item no longer invalidates it(good), but it does allow it to be selected again(bad)

Conclusion?

As far as I can tell there is no way to provide a dropdown list separately from validation, and no way to apply multiple validations on the same cell. I thought perhaps there might be some way for a custom formula to provide separate lists for the dropdown and for the validation, but if there is I'm not finding it.

The closest I've come is creating a separate dynamic list for every dropdown (dependant on those above it), but that would be massive considering the actual size of the dataset, dropdowns, actual dynamic filter, and would bog down the app window... I really need a better workaround and I'm hoping one of you kind folk has it.

ETA: sample sheet of my partial solution

Answer 1

the only way how one cell can have more than one data validation is to use proxy data validation from another cell on that cell. let's say cell A1 has set data validation from a list of items and those items are 1,2,3,4. then you can set proxy data validation from (on) B1 cell with a custom formula validation like =ISODD(A1) creating double data validation for cell A1.