Information – Legend of the grid: are there any rules around?

I have a grid and I'm thinking of adding a legend. Like there are legends for the graphics.

This is what would go in the legend:

  1. 70% of the columns are editable. The known pattern would be to place a pencil icon in each column. But I end up with an army of pencils … 🙂

  2. Some line items are missing data. I need to label them, so the user knows.

  3. There is a column where the content can be added; not edited

I thought about coding these 3 things by colors. But, now that I think about it, I need a way that does not depend on color to communicate this information, for ADA purposes. So, I end up with icons, anyway …

Right? Any ideas?