OK, so there is a Core 6K, Core 2K, Core 2.3K, Core 10K, and a Core 5K decks. And Ankidrone Starter Pack.
-- Core 6K: The original iKnow word list, with 6,000 words based on newspaper frequency from the 90s.
-- Core 2K: Only the first 2,000 words of the Core 6K, since most people stop learning from fixed list after roughly the first 2,000 words and instead start making their own flashcards.
-- Core 2.3K: Also a ~2,000 word subset of the Core 6K, but chosen by frequency in today's popular media, like light novels.
-- Core 10K: The Core 6K + an additional 4,000 less common words added from another resource.
-- Nayr Core 5K: A separate effort, not based on the iKnow word list but on the A Frequency Dictionary of Japanese book.
-- Ankidrone Starter Pack: Also separate, based on the popular Tango books with word lists from the N5-N1 JLPT exam levels. Around 8000 TSCs in total across all 5 levels.
Now, all "Core" decks suffer from a number of common problems:
1) words taken from newspapers from the 90s are just too useless no matter how you sort them with frequency lists.
2) the example sentences overuse pronouns that are not used in real japanese that often
3) card templates. you have a word on the front of a card, as opposed to having a sentence on the front with the target word marked bold.
I hope that clears things up ...