The RPGA and DCI databases merged last August.
All RPGA numbers are now ten digits long. However the first digit is (I think) a calculated check-digit. You can actually log in with the last nine digits, or with all ten digits. This means you can turn an old RPGA number which is less than nine digits long into a working number by adding a '1' at the front then as many '0's as needed to make the number up to nine digits. You can then log on, presuming you still know your password.
As an example, my RPGA number was 9536692 (7 digits). Once the database merged I had to append '10' to the front to make 109536692 (9 digits). Once I log in my full RPGA/DCI number is displayed, which is 1109536692 (10 digits). I don't actually have to know or use that - the leading '1' is superfluous.
Should this not work, or the system not accept a password, I would contact WotC Customer Services at
www.wizards.com/customerservice If the 'Email Us' tab is not working for you, see this thread:
Trouble Accessing our Help System? Post here. - Wizards Community for details of how to get that fixed.
Finally (!) now the databases have merged, anyone who has access to an up to date copy of the DCI Tournament Reporter program can retrieve people's DCI numbers if given their names and locations. I've got a copy on an old computer - I'm happy to look people up if they email me (pete@pedrg.eu)
(Edit to add: I think that very old
DCI numbers were converted to
eight digits at some point, which might explain the six-to-eight conversion mentioned above. Very old
RPGA numbers (and I have some friends who had three-digit numbers) had to be turned into nine-digits numbers to log into the new system).