Creating a Queue

Hi everyone, I was hoping to try and get some help with a problem that I have been stuck on for a few days. I need to create a formula that acts like a queue of where a part currently is in a process. There are multiple operations and not every part undergoes the operations in the same order. Some parts go through one operation multiple times.

I wanted to create this formula by finding the first blank date and then producing the value that would be in the column to the left of that first blank cell. For example, in the attached worksheet I would need part M1 to produce “Review” in the cell as every operation before review has a date that follows it.

Any help with this problem is much appreciated.

This is awesome. Thank you!!