I don't use "To Whom It May Concern" as a salutation. If I were to use it as a salutation I would write "To whom it may concern." If I know only the organization or business, I write "[Dear] org/bus representative". (e.g. Dear Red Cross representative; Dear Kiva.org representative; Amazon.com representative). If I want to express the thought of "to whom it may concern" I use "to all concerned." As a salutation, I capitalize only the first letters that would be capitalized in plain text: the first letter and proper nouns and titles.
So my generic reference letters start:
"To all concerned,"
That is my own, personal style.
 It's a surprise to me that the capitalized version goes so high in this Ngram. Maybe a lot of it are titles or headlines.
Would you link the episode.
Now 'To all concerned' sounds a bit like some kind of edict from high authority. Just me.
I just go with "Greetings:". (I guess only the older generations would think of the Draft.)
That one started with "Greeting". I ignored it.
Did you get one in lower case? The upper case looks a little harder to ignore. One GREETING: from one (Sam) to one about one BIG business.
 (There are many picts. I don't know if it's illegal to post or just my iPad.)