When did it become Pennsylvania (with three n's)?
While English spelling became more and more standardized after the printing press was introduced in 1475, it was not considered important until the 19th century. In the U.S., universal standardization was spurred by Noah Webster's ideologically motivated 1783 speller and 1828 dictionary, and by Horace Mann's efforts and the start of universal public schooling in various states from the 1830s onwards. The dictionaries did not include proper nouns, so names were among the last words to get standardized spellings, as any exasperated genealogist sifting through old passenger manifests and Census data knows.
Probably a dozen forms were in use in the late 1700s. Both Pensylvania and Pennsylvania appear on the original U.S. Constitution, notable as not only was the document composed in Pennsylvania, but the secretary, one Jacob Shallus, was a scribe for the Pennsylvania state legislature and presumably one who ought to know.
Multiple spellings frequently appear in the same document, sometimes just a few words apart:
… or no words apart:
Indeed, Seymour Stanton Block's 2004 biography of the commonwealth's most famous son, entitled Benjamin Franklin, Genius of Kites, Flights and Voting Rights, reports that as an anti-counterfeiting measure,
The Spanish labeled the area L'arcadia, or "wooded coast", during the explorer Verrazano's voyage in in 1524. (This is significant.) After changing hands multiple times, the land was given to Willian Penn by King George II to settle a debt owed to Penn's father by the king. Though Penn suggested Sylvania (Latin: silva/silvestre means woods/forest. Sylvania means woodland.) I seem to remember it was George himself who named it Penn's Sylvania (later shortened to Pennsylvania).
Back when the bell was made (actually for many years before and some after), spellings did not matter as much as sounds. The word Pensylvania and other variants all appear on old maps and documents.
This spelling has been used to illustrate the doctrine of idem sonans in law, which provides that the misspelling of a name is acceptable on a deed so long as it sounds enough like the owner's name. Similarly, in the first line of the "Frame of Government of Pennsylvania adopted May 5, 1682," the colony is spelled "Pensilvania." However, it was not so officially named.
The bellmaker, however, copied the name in the quotation, stating "By Order of the Assembly of the Province of Pensylvania for the State House in Philada." No one assumes, however, that Philadelphia was ever actually named Philada. All throughout history, when things were written (or carved, etc.) by hand, especially when they needed to fit into limited space, abbreviations and misspellings are multitudinous.
Medica's statement about the provenance of the name Pennsylvania is absolutely correct.
Pensylvania, however, was an accepted alternative spelling at the time of the casting of the Liberty Bell.
This is referenced to: