yeah, I got my 5th kyu like that. My sensei always does two or three grading sessions during grading week so that all can attend. However I was working shifts at the time so I missed them all.
So we agreed that I could do my grading on a weekend training or something, but at the end of the class we all sat seiza and he called me and one 3rd kyu guy up. I though we were just going to demonstrate some techinques, but realised quicly that I was going to be graded there and then.
A bit surprised really, and I had not gone through the syllabus as I normally would. But it went fine.
Now that was 1 year ago and I still havent gotten my 4th. Blerg! Must practice more regularly.