Katakana spelling changes

I've seen changes in English spelling from time to time, but I was surprised to see a change in a Japanese Katakana spelling. I had to translate an American's business card into Japanese, so I wanted to ensure that the words I was using were correct. I looked in a Katakana dictionary that was revised in 1994 (the original publishing date was 1972), to check the correct spelling for the word "fax". The dictionary spells it like ファクス (fakusu) but there are a lot more spellings like ファックス (fakkusu) on the Internet, even at companies that manufacture fax machines.

There's also another Katakana spelling that I found that's questionable, which I'll talk about later. Hint: a weird ingredient in gum.