Calculated column from final acceptance date based on specific previous period from same table

Hello,

I would like compare the [Final acceptance date] from a current line item with the baseline, where the budget was created.

This information can usually be found in the project specific line item of the project, where [Date Key] = 30.09 of the previous year and i would like to write this [Final Acceptance Date] into into a calculated column called [Final Acceptance Date (Baseline)].

If there is no dataset available for September of the previous year, the [Final acceptance date] based on the earliest available [Date Key] for the specific project should be used. Only line items where parameters  "Role" = "relevant" and Type = "month" are relevant in this context - the others should be ignored.

Example 1:

For [Project Number] = "123" and [Date Key] = "30.04.2021", the correct value for the new calculated column [Final Acceptance Date (Baseline)] would be 15.10.2021 ([Date Key] from 30.09.2021).

Example 2:

For [Project Number] = "456" and [Date Key] = "31.03.2021", the correct value for the new calculated column [Final Acceptance Date (Baseline)] would be 02.10.2021 ([Date Key] from 28.02.2021).

I tried to solve this with LOOKUPVALUE in combination with MINX+FILTER for example, but i wasn't sucessfull. 

I would highly appreciate if you could help me to solve this problem.

Thank you,

Best regards,

Reinhard