I'm familiar with the usage of かどうか for "whether or not," but I can't understand its usage in the following example:
部の記録見る限り７０符なんて千局に一回出るかどうか
Is this an idiomatic usage of it? Since I'm pretty sure its supposed to indicate that the probability is even less than 1/1000 games.
だ or です is omitted after this かどうか. The more canonical version of this sentence is like this:
部の記録を見る限り７０符なんて千局に一回出るかどうかだ。
This sentence means "the probability is 1/1000 or even less" rather than "the probability is even less than 1/1000". You can think of this Aかどうかだ pattern as "A, or even worse" or "may or may not A".
See this question for more examples: Understanding ～かどうかだ
