I am also working on a previous story that I have prepped at least once, if not twice. I find doing the assignments helps me find my way back into my story - I had stuff stolen in January and it knocked me for a loop. Finding my way back in is important.
I tend to do the assignment and then check the previously done one to see how close my vision is, or how much its changed based on how much work I have put into it.
Keep at it.
I love the colour coding system. That took a lot of work.