"I need to store multiple dates in the table is the reason for the 4 fields"
Unfortunately, multiple date fields for the same data is an inappropriate table design for a relational database application.
In turn, that table design forces you to adopt workarounds like this one to try to manage the data.
You've been given a workaround that allows you to preserve that flawed table design, but that is not really the most appropriate way to handle it.
These dates should be in a child table called something like "TaskCompletion".
In that table you need one field for the foreign key to the task table, one field for the Quarter, and one field for the actual completion date.
There are many excellent resources available on the internet to help you learn how to properly design tables for a relational database application. The process is called "Database Normalization", to distinguish it from other sorts of "normalization".
You would probably benefit a lot from investing time to learn about Database Normalization and applying it to this project. Otherwise, the workarounds needed to manage inappropriately designed tables keep getting in the way of productivity.