Removed 島 from the index as 木曜島 is a proper noun.

Not sure I agree with that. Pretty much all examples of 島(とう) are part of proper nouns - but they are also examples of

島 【とう】 (suf) island (in placenames)

As long as 木曜 isn't indexed I don't see the harm.

OK. My index-checker picked up that 木曜 was missing, and I wasn't
that keen to add it to my stopwords file. I guess it won't hurt.

I also removed ヨーク岬 and トレス海峡. I can put ヨーク and トレス in the stopwords if you want to reinstate the 岬 and 海峡.

Ah, a 'technical limitations' thing.

I used to have one with the 'no index' method I used. With sentences like ...

はるかはこないだろう。

I would surreptitiously change the name to katakana to stop it picking up the earlier は in the name and getting confused.

It would only be a problem if a *real* 木曜 was missing from an index. Then I'd ignore it. Since there are plenty of 島 【とう】
examples which won't have that problem (Bali, Elba, Wake, etc.)
it might be best to treat it as 木曜島 and leave it out.