The findings related to notification illustrate there is much work remaining for public safety agencies in educating citizens on the tools and processes for getting the word out. While the question was not posed exclusively to citizens within jurisdictions having a traditional ENS (and therefore, we can't say 50% of people in communities with an emergency notification system DO NOT know about it), it nevertheless points to needs for local agencies to communicate their outreach methods whatever they may be.
This is a constant challenge. Many agencies struggle just to have enough budget dollars for system acquisitions or ongoing maintenance. Money for community awareness just isn't there. Often, however, large communication budgets are less necessary than focused efforts and a little creativity.
"Branding" a communication campaign and exploring relationships with civic organizations, religious institutions, local business, press, etc. may yield positive results for little or no cost. Agencies should remember it takes multiple exposures for people to absorb any message, so diverse communication channels should be deployed. Persistence is key (keep pushing the message out even if you're sick of hearing it internally: it's just beginning to work at that point).
Educated citizens can make the response to a critical situation safer and more effective. Efforts focused on increasing public awareness of notification methods will pay dividends in the long run.
All the best,