the coreplus anki deck has a load of tagged duplicates, "rｔk2duplicates" and "koreDuplicates". Is there some reason these have been tagged rather than deleted?

I can't see the reason, but it could be that the duplicates exist because while the word is the same; maybe the word has two different meanings that get used often in various situations. So the word is in the deck twice with a different sentence each time as a way to show the difference. Just a guess though.

The first lot of facts in the coreplus deck were imported from the 'core spreadsheets', which had 6000 words, each with example sentences. Some of those words were duplicates in kanji and kana but not meaning, eg. 起きる to wake up, 起きる to happen. These will be the ones marked duplicates. The RTK duplicates account for the fact that I tried to include each word in the book, with its frame number (field named rtk), so as to be able to sort on that field and work through the words in order if desired. Some words, however, were included more than once in the book. There will also be other double entries that are not marked, where a word was already in the deck in kanji form and was then imported from a JLPT word list in kana form.