completion date per user id

Hi,

I have several registration processes I work with. Some of these processes have 4 steps, some have 3, and some have 10. I have a table with a unique identifier of the registration process and the step, along with a column that tells me if this was the last step in the sequence. The following table shows two registrations (A and B). Registration A contains of 4 steps, of which step 3 is considered the last step. Registration B contains 3 steps of which step 2 is the last one.

I have a table showing me all the steps my users completed. The Registration step is linked to the other registration step table.

I now want to add a calculated column that shows me for each line of the user what the date was when the last step of the registration got completed. This is what I want to achieve:

I tried the following calculation, but it then only shows me the registration completion date for the line where the registration got completed. 

CALCULATE(
    FIRSTDATE('Main Data'[step completed date]),
    ALLEXCEPT('Main Data','Main Data'[User ID]),
    filter('Registration step',RELATED('Registration step'[is last step])),
)

I need this date to show up for every line of the specic customer, just like in the example.

What would be the right way to achieve this?

Best regards

Bas