I was just double checking english.txt for list of stopwords as I felt it was taking out valid tokens like 'won'. I think issue is english.txt list is missing apostrophe character and all character after apostrophe. So "won't" becam "won" in that list; "wouldn't" is "wouldn" .
Here are some incorrect tokens in this list:
I think ideal list should have both style. i.e. won't and wont both should be part of english.txt as some tokenizer might remove special characters. But 'won' is obviously shouldn't be in this list.
Here's list of snowball english stop words: