Or, what to do about variant spellings.
This advice brought to you by OK/O.K./okay, that typically American and variously-spelled affirmative. All of the above spellings are acceptable, but you will not make your copyeditor happy if you use more than one of them in your manuscript. (And using ok in lower case is also iffy.)
Which one you prefer to use is your own business, and you can make the choice on the grounds of what you think looks good, or what you were taught in fifth grade, or what you will. (I chose “okay” on etymological grounds, because I prefer the theories that derive “okay” from either Native American or African terms to the theories that derive it from abbreviations of various American English phrases such as the humorously-misspelled “Oll Korrect”†or the nickname “Old Kinderhook”‡ — if you’re interested in the arguments on the subject, there’s a pretty good summary here.)
Just be consistent in using whichever one you decide works for you. You can get away with a great deal, at least in dealing with editors and copyeditors, so long as you make consistency one of your virtues.
†Well, people thought it was humorous at the time. Fashions change, and a good thing, too.
‡Martin van Buren.