I'm really sorry to have to ask this question because I am sure it has been asked and answered a million times. Trust me, I searched, but "K" and "KA" are just too short for search engines. I read the Ultimate Guide, too. So, having apologized profusely... Can someone tell me what the "K" and "KA" mean following a model number? I'm specifically looking at a couple 4000 automatic watches, e.g. WF2121-K and 695.706KA (the "A" is not dyed/colored). Thanks!