Charles, I have had the same frustrations at times. And I've also had to deal with internal questions such as yours. There certainly is value in progressing up the ranks; I'm not suggesting that anyone should not care about promotions. I know that I did, and I also wondered how long it would take me to reach yudansha ranking. For myself, I took some satisfaction in being able to "hold my own" while training with higher ranking Aikidoka. I was also fortunate to have Sempai who understood the situation and arranged for me to test for some ranks outside the normal parameters. If it doesn't make you uncomfortable, perhaps you could ask to test for the kyu that you would hold had you not missed any test dates.
Stephen: We have similar guidelines as well...a certain number of calendar time must pass before you can test for the next kyu, and you must have logged a certain number of hours of consistent training. These are minimums. However, there is a roster posted a week or so before each test date (there is a kyu test every three months or so), and if your name is on it you are expected to test. We do have to apply for Dan testing, though.
I have also witnessed the following scenario happen to students who do not show up for tests:
A normal class begins and everyone trains. With about twenty minutes to go and without warning, so-and-so is called up with an uke and tests right then and there
Imagine that during a 7:00 A<M< class
Anyway, good luck with everything. We are all beginners, just at varying levels.