I passed my VCAP4-DCD (when still in Beta exam) and get the certification number: VCAPDCD-8.
When I passed the VCAP5-DCD exam on March 2012., VMware give me the same certification number: VCAPDCD-8.
Now, according to VMware, they streamline the certification exam registration process, and provide us a single consolidated view of our training and certification histories, they have updated the candidate tracking systems. Now, my candidate ID become VMW-00087451L-00017218, according to VMware they will start using the new candidate ID to replace existing VCP ID & VCAP number.
VMware still keep my VCP ID (or certification number) 17218 in the new candidate ID (the last few digits 00017218), but not sure about the VCAPDCD number; just wonder whether the VCAP is the middle number "00087451L", then what does 7451L stand for? 
Most importantly, we get certified and able to demonstrate our skills & knowledge; the certification ID is just a reference ID. 