For much of the medieval period, the only way to disseminate knowledge (scientific or otherwise) was by personal letter or in books. In a very real sense, this preserved the traditional structures of authority, knowledge, and even doctrine.
In his book, Radical Enlightenment: Philosophy and the Making of Modernity 1650-1750, Jonathan I. Israel argues that the development of scholarly journals served to upset these structures and so accelerate the development and expansion of knowledge.
I'd like to illustrate the situation before the introduction of scholarly journals with a couple of examples.
Roger Bacon was a Franciscan friar and philosopher in thirteenth century England. He is probably best known as being the first person in Europe to record the formula of gunpowder. He emphasised the study of nature through empiricism and was one of the earliest European advocates of the "scientific method" inspired by Aristotle. As such, we can probably reasonably classify him as an early scientist.
This was long before the invention of the printing press, so his work would have been transcribed - by hand - in the scriptorium of a monastery. The amount of work involved in the transcription process, by its very nature, limited the number of copies that could be produced. In turn, this was a real limitation on how widely the details could be disseminated. In that context, the idea of a "learned community" in the modern sense is probably anachronistic.
Despite this, some news of Bacon's research and discoveries would have been transmitted by word-of-mouth and by letters. That news certainly travelled all across Europe, for we know that Pope Clement IV requested a copy of Bacon's work. A copy of his Opus Majus, was sent to the Pope in Rome in 1267.
Another Englishman, who was also a practitioner of the scientific method, was Francis Bacon. He was active during the early part of the scientific revolution, some 300 years after Roger Bacon. Despite the earlier work of of Roger Bacon, it is Francis that is today often called the "father of scientific method" and "father of empiricism".
This was not because Roger Bacon's work had been lost. It simply reflected the increased range that could be achieved in the years after the development of the printing press. Although this was after the medieval period, it was still before the days of learned societies and scholarly journals. His works were published privately. However, in some ways, it can be argued that it was the work of Francis Bacon that led to the publication of those journals.
The Royal Society is, perhaps, the oldest learned society still in existence. It was founded in November 1660. Its founding members claimed to have been influenced by the "new science" - that was promoted by Francis Bacon in his New Atlantis.
As to the question of why medieval Norsemen who visited North American were not credited with its "discovery", that is probably largely due to the prevailing attitudes in Christian Europe.
Most texts were written by men of the Church (which brings us back to those "traditional structures of authority and knowledge" I mentioned above). Given the depredations of Viking raiders against Christian Abbeys and Monasteries, it is probably not surprising that they were rarely reported in a positive light. In all probability, few had even heard of the Norse sagas, even fewer thought they were worth recording. Because their settlements were ultimately unsuccessful, the story was simply lost.