The above are but four of many sources mis-crediting Magellan or his crew with bestowing the San Julián place name. This page presents some evidence that the name was in existence for some years before he wintered there.
In his letter to the Cardinal-Archbishop of Salzburg, Maximilianus writes of the Magellan expedition, that “… not till the last day of March of the following year  did they reach a bay, to which they gave the name of Saint Julian.”
On October 23, 1522, in a discourse on Magellans's voyage, Gian Battista Ramusio, who had not taken part in the expedition, said, “not till the last day of March of the following year did they reach a bay, to which,” he carelessly added, “they gave the name of Saint Julian.” This was the first appearance of this error.
Actually, Ramusio simply referred to the Maximilanus letter in his “Discourse,” but was of course not its author.
In any case, the “…gave the name” phrase is a typical example of a place named by a member of an expedition. For the Magellan expedition, see Strait of Magellan on the Place Names page for several more examples, each of which makes it clear that the name originated on this expedition. But in contrast to this practise, although several writers mention San Julián by name, none claim that they named it:
In context, each writer seems to refer to a place previously named by someone else. In further support of this, Bautista's account lists numerous places visited during the voyage:
If the Magellan crew did indeed name all these places, it would be unlikely that this writer would make that claim for all but San Julián. Also, there is one feast day in February and three in March dedicated to various St. Juliáns (see list), but none fall on the expedition's day of arrival—31 March, according to Albo and Bautista—and it would be quite unusual to name a place after a saint whose feast day does not coincide with that day. It is therefore an unlikely name to have been bestowed by someone in the Magellan fleet.
|San Julián Feast Days|
|12 February:||St. Julián the Hospitaler|
|8 March:||St. Julián of Toledo|
|16 March:||St. Julián of Antioch|
|23 March:||St. Julián|
But then, how does one account for the statement by Maximilianus? Unless someone in the expedition gave him specific details which were not recorded in any first-hand account, he may have simply made an erroneous assumption, which eventually found its way into Richard Hakluyt's 1589 Principal Navigations.
Also worth noting; when Sir Francis Drake's nephew, also named Francis Drake, compiled his The World Encompassed, he included a description of the 1578 arrival at San Julián. For comparison purposes, both are shown here:
|Hakluyt: Principal Navigations||Drake: The World Encompassed|
“The next day after, being the twentieth of June, wee harboured ourselves againe in a very good harborough, called by Magellan Port S. Julian, where we found a gibbet standing upone the maine, which we supposed to be the place where Magellan did execution upon some of his disobedient and rebellious company.”
“Thus the next day the 20. of June we entred Port Saint Julian: which standeth in 49. deg. 30. min. and hath on the South side of the harbour picked rockes like towers …”
Note that Drake the nephew makes no mention of Magellan which, although inconclusive, may further support the notion that both Maximilianus and Hakluyt were indeed mistaken. But if so, who then did bestow the name?
One possible candidate is Amerigo Vespucci, who sailed down the coast of South America (his third voyage, May 1501-September 1502). According to The First Four Voyages of Amerigo Vespucci (Michael Kerney translation, p. xxxi), he sailed southward until reaching South Georgia (52° S) on April 7. Perhaps he reached San Julián in February or March (see list above), named it, then continued on his way.
Juan Sebastián del Cano biographer Mairin Mitchell states (p. 47) that:
Amerigo Vespucci, in his third voyage to the New World … claimed to have reached a point as far south as 50° 40', i.e. beyond the latitude of Santa Cruz in Patagonia.§
§ Actually Vespucci wrote, in a letter to Lorenzo di Medici, that he reached 49°, and later in the same letter, 50° South Latitude (See list below). In any case, Santa Cruz is about 60 miles south of the Bay of San Julián, which is at 49° 20' S.
Unfortunately, most accounts of Vespucci's third voyage—including his own—are maddeningly vague or contradictory, as noted by conflicting claims of his southernmost latitude—again, including his own:
If the data in Vespucci's “Magnificent Lord” letter (see link above) is reasonably accurate, he may very well have been near (or at?) Bahía San Julián on one of that saint's feast days in February or March. In fact, one clue that the name may be his will be found on the so-called Turin Map. The detail view (magnifying-glass icon at bottom of map) shows “Baya de San Giuli_” (not “Porto di San Giuliano” as stated by Frederick J. Pohl, p. 122). Although the final letter is unclear (“a?”) and additional letters are missing, the “San” indicates a male saint, and “Giulian” or “Giuliano” are the the Italian equivalents of the Spanish “Julián.” Although the evidence, such as it is, is not conclusive, it does present a reasonably strong case for Vespucci.
Other candidates are João de Lisboa and Estevão Frois: between 1511 and 1514 they were known to have been in the area of Rio de la Plata and Golfo de San Matías, and may have been as far south as San Julián, and possibly even beyond there. João de Lisboa and Magellan were acquainted, so perhaps the one told the other about a bay named San Julián.
In any case, the name of the bay seems to predate the arrival of Magellan in its waters.