Networking and word of mouth is a big investment. Don't waste time and money, and lose out on sales opportunity, by sloppy record keeping. Use a reliable tool to record and track all these highly valuable contacts.
I have found that routine emails or other "touches" is important if you want to keep these contacts viable. I call it shelf of mind (https://www.theoryaboutthat.com/faq#Be-Shelf-of-Mind)
I recommend to my clients that they use something simple, cloud based, and free to accomplish both contact tracking and email management: MailChimp. (http://www.mailchimp.com ) . The free tool includes a database, and a limited number of emails per month.