Since the app gives you the words to say, and translates those back to coordinates on the receiving end, in theory they could alter the word list, at the cost of making any written-down version obsolete.
Maybe they should release a new service called What4ActuallyVettedWordsAndWordCombinations ;)
But it's worse than that, there are confusables within small distances of each other:
https://cybergibbons.com/security-2/why-what3words-is-not-su...
https://w3w.me.ss/