Yellowing Boxwood Hedge
This information from another state in included because it is very thoroughly researched and provides several reputable resources including the Boxwood Society that is a new and importsant resource to be aware of. It may be that this blight issue though relatively new to Oregon is not relevant to your question but the suggestions for care and treatment should be a valuable and ongoing resource for you with your numerous plants and their location in your landscape.
Here are two sites that will provide information regarding winter burn and how you might prevent a recurrence of events during the upcoming 2019-2020 winter:
There is a blight (fungal disease) that can infect boxwood and cause browning of leaves. This is a possibility for your boxwood. But if this was the case, I would not expect to see the vigorous, new growth at the base. Yet this is something to consider should you see additional leaf browning. If this occurs, please get back to us. Here is some information about this blight:
Once all dead branches have been removed, be sure to keep things well watered. This will encourage additional vegetative growth. Adding fertilizer now should be done. Do not delay this too long. It will be most effective when the boxwood is showing vigorous growth. Use a fertilizer that has a high nitrogen content. 10-10-10 garden fertilizer would be a good choice. It should be available at any garden center or big-box store. Water it in well.
Here is another site that might provide you further information about your boxwood (several links are available at the site)
I would refrain from doing any extensive pruning at this time other than minor shaping. Here is a site that contains great information about pruning boxwoods: