For the Portolan Context See: The Maps of King Arthur? - The Inventio Fortunata
By taking measurements with the astrolabe it is obvious that the author of the Inventio intended to collect data for a map. He either supplied the book with a map or left it for readers to draw one. Either way the presentation of Hudson Bay on 16th century maps (see here) suggests either only partly transmitted classical information or the Inventio as source. Most likely the author of the Inventio was in summer 1362 part of the "10 men (left) by the inland sea to look after our ships" like the Kennsington runestone mentioned.
To get the feature of Hudson Bay on our maps this party has to be back in Vinland by late 1362 because they had no chance to survive a winter at Hudson Bay. In 1363 a Norse long ship brought a missionary priest back from Yucatan to Vinland. It seems the author of the Inventio was onboard this ship too. He took the whole voyage from Vinland through Florida Strait to Yucatan and back. In 1956 E. Roukema published an article "A Discovery of Yucatan Prior to 1503" in Imago Mundi.
He noted a Yucatan like feature on several maps before the official discovery in 1517. On the c. 1505 Caverio map he analysed the names along the coastline. Compared with the British Admiralty's West Indies Pilot (Vol. I, 8th edition 1923) the names described real features like capes, lagoons, river mounds, islands, reefs or landmarks.
Roukema: "To sum up, the conclusion that prior to 1503 European navigators explored the shores of the Gulf of Mexico and the Caribbean, from Punta Arenas in the west to a point between Cabo Camaron and Cabo Gracias a' Dios in the east, is certainly surprising. But in view of the facts presented there can be no reasonable doubt that such an exploration actually occurred."
Roukema tried to find evidence for a Spanish, Portuguese or even English mission to the area but without success. He could only conclude that this map "came from a clandestine source" the mapmakers of the 1500s no longer had contact with.
According to Roukema the distortion in east-west direction is easily explainable by the prevailing winds. The dominant winds there are from the east. The journey from west to east against these winds "threw the pilots' dead reckoning out and produced the exaggerated estimates of coastal extension referred to." For that problem an astrolabe was of no help.
Roukema searched the records about voyages around 1500 and had no chance to suspect the Inventio. Because of the wrong information the Inventio would only describe the area north of 54 degrees. That was probably an intentional deceit by Ivar Bardsen to Cnoyen to prevent voyages to Vinland - a policy well established then. By his nautical knowledge and looking at all historical evidence Roukema could only conclude about this expedition: "It is reasonable to believe that the unknown discoverers came from the direction of Florida Strait." Coming from Vinland that was the only way.
Some place names indicate Christian days of the year. That way we know they made landfall at northern Yucatan on a specific day in Lent, left before Easter Week and went south to Honduras and ended the exploration there after June 18. Several dates were fixed days in the calendar but some refer to the Easter Feast that moves from year to year by a complicated formula. By correlation of geo location with fixed and movable dates it seems possible to calculate the probability of the year it happened.