The general rule is, if the letters are pronounced phoenetically together as a word, it counts. That's why Scuba and Laser are in. It's the difference between AWOL (in) and MIA (not).

OK was never accepted before because it's not said as "ock". UV isn't pronounced "uhv" so should also be excluded. I guess now the distinguishing feature between those cases is that UV is an initialism while OK isn't. I can't think of any other example like OK, a word that is not an initialism and is said by naming each letter rather than pronouncing them phonetically.

Ko is in for being a (loan)word in its own right, not as the two-letter abbreviation for "knockout". https://en.wikipedia.org/wiki/Ko_fight