Mark,
Great questions - I'd love to hear and learn from others as well.
Based on my limited knowledge/research, moving forward, 3rd party lists will no longer comply with any form of consent, regardless if Data.com has gained their own consent. The only way you can get a contact from someone else is through 'referral'. The referral must be from a person to a person - not from a company, and in your email to the end customer you have to acknowledge who you got the referral from.
With regards to grandfathering in - here is the run down.
Prior to July 1, 2014 - any person whom you had implied consent, you will have implied consent for them for a period of 3 years, until July 1, 2017. This includes 2 forms of implied consent:
1. an existing business relationship i.e. they've purchased something from you or signed an agreement.
2. The recipient has made an inquiry in respect to above - any time in the past i.e. question or request for information to make a purchase.
The catch to the above is that you should be able to prove that you gained implied consent and the date you gained such consent i.e. a form submission or inquiry date etc.
After July 1, 2014 for implied consent #1 above gives you 2 years of implied consent while #2 only gives you 6 months. In all 4 cases, you can send an email whenever you want to try to gain express consent prior to their 'expiration' date.
Express consent is forever, however, this needs to be proven that the person has filled out a form that meets the criteria of non-prechecked box etc.
Hope that helps!
Regards,
Aziz Nana