Lorien: is your certificate from Hombu dojo / aikikai in Japan ? if so your book should be somewhere. If not then your grade is not 'as such' recognized with the official hombu dojo.
It should look somewhat like those you can find on this page: http://www.frederiksberg-aikido.dk/sensei-selene-thomas
If you wish to enter the Aikikai by joining a dojo affiliated with them, then any grade from some dojo outside the organisation must be 'transferred' - or more likely re-taken.
If you have never been told about these things in your 'old' dojo then I would venture the guess that it is not part of the aikikai organisation. I am under the impression that there is a growing tendency in the US to break away from hombu dojo, but that is a different discussion.
Read more about Hombu dojo / aikikai here: http://www.aikikai.or.jp/eng/