Actuall, the "33" is not a mystery. Excerpted from a Cecil Adams column ("The Straight Dope"):
I hunted up James L. Tito, who at one time was chief executive officer of Latrobe Brewing, the maker of Rolling Rock beer.
Mr. Tito's family owned Latrobe from the end of Prohibition until the company was sold to an outfit in Connecticut in 1985. After some prompting, he told me the sordid truth.
Based on some old notes and discussions with family members now dead, Mr. Tito believes that putting the 33 on the label was nothing more or less than a horrible accident. It happened like this:
When the Titos decided to introduce the Rolling Rock brand around 1939, they couldn't agree on a slogan for the back of the bottle. Some favored a long one, some a short one. At length somebody came up with the 33-word beauty quoted above, and to indicate its modest length, scribbled a big "33" on it.
More argument ensued, until finally somebody said, dadgummit, boys, let's just use this one and be done with it, and sent the 33-word version off to the bottle maker.
Unfortunately, no one realized that the big 33 wasn't supposed to be part of the design until 50 jillion returnable bottles had been made up with the errant label painted permanently on their backsides. (I suppose this bespeaks a certain inattentiveness on the part of the Tito family, but I am telling you this story just as it was told to me.)
This being the Depression and all, the Titos were in no position to throw out a lot of perfectly good bottles. So they decided to make the best of things by concocting a yarn about how the 33 stood for the year Prohibition was repealed.
Count 'em:
Rolling Rock from glass lined tanks in the Laurel Highlands. We tender this premium beer for your enjoyment as a tribute to your good taste. It comes from the mountain springs to you."