I don't think the RIM certifications expire (much like those of Cisco) so once you pass a test you will be BlackBerry certified, I have not seen anything stating RIM will expire/void any certifications yet.
Of course it would be good practice to stay current.. but once you know BlackBerry it's almost all the same, they just move stuff around on us.
8830 -> 8330 -> 9550 -> 9650
Just think about how far BlackBerries have come from then till now... And what else is coming.
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