EveryDNS does not use the recommended format for serial numbers. If we did, it would only allow for 100 changes a day. Since we believe in letting you change your records more than 100 times a day, we cannot conform to this. This, in most cases, will not cause any problems in the use of your domain.
You might want to visit http://www.dnsreport.com/ for each of your domains, to verify that it shows no red error messages.