Need to make a column dependent on another...?

[dmcquaw]

I have a spreadsheet for work that we use to track device assignments using information like full name, email, Serial Number, Model, etc. We also have a column for previous models if the original was replaced. This is the trouble column. If I filter by last name to clean up the list the previous models do not sort with the rest of the sheet.

It ends up looking like this:

You can see that the names in the left most column do not match the information on the right. There are a lot of empty cells as not all devices have been replaced, but I'm hoping there is a way to calibrate the right most column to be dependent on what is in the left most column so that I don't have to manually rearrange all of the data on the right.

Thanks!