I cannot say about other countries but here in the US I don't think you should wait because Prometric uses Social Security number to identify you because I took seven exams back in 2000 and when I registered for the current six exams I did not provide my MCP ID but prometric had provided both my MCP ID and Social Security number to the testing center when I showed up to take the first two of six. Below are the email addresses to contact for MCP ID the first is for the US and North America and the second is for the rest of the World but I could be wrong about the second.
mcphelp@microsoft.com
emeamcp@msdirectservices.com
An Elliptic curve is modular ~ Taniyama and Shimora