Citations are individual instances of words in use and collections of these also have no claims to be corpora. The precise conditions for a valid sample size for a corpus are indeed under discussion --- see later --- but no-one concerned seriously with corpora has attempted to gather a collection of ciations and announce it as a corpus. What has happened is that owners of previously-gathered citation collections have tried to use them as a bridge between traditional practice --- particularly in lexicography --- and corpus-based work.
It is unhelpful to confuse categories in this way, and important to assert minimal criteria for use of the word `corpus'.