So, did the Portuguese reach and chart Australia's east coast?
There is no direct evidence to support the notion that they did, and it's unlikely that any will ever emerge. The 1755 Great Lisbon Earthquake destroyed the repositories where the relevant charts and documents were archived.
Still, there's a definite consensus that they might have.
Based on the Dieppe maps, the cartographic evidence is questionable at best and remains a matter of debate.
However, it seems safe to assume they knew the continent was there, even if they didn't reach it.
In the end, the question becomes this: Is it possible to build a circumstantial case for a possible Portuguese discovery?
My answer is Yes, on several fronts.
Matters discussed in When Is Something 'Discovered'? suggests they had form in this area. Dynastic intrigue on the Iberian peninsula, Fernão de Magalhães' switch to Spain, and the possibility that the Spice Islands might lie in the Spanish hemisphere under the Treaty of Tordesillas all contribute to a motive.
We also have names. Cristóvão de Mendonça sailed from Goa with four ships bound for Malacca and points beyond in 1520. His carrack was part of the seventeen-ship Armada that sailed from Lisbon in April 1519 as Magellan was preparing to sail from Seville.
Mendonça's official objective was the Islands of Gold (the Ilhas do Ouro). They appear in ancient Indian literature as Suvarnadvipa or Suvarnabhumi and Graeco-Roman geography as the Islands of Gold and Silver and the Golden Chersonese (Chersonesus Aurea).
A previous quest for the same objective under Diogo Pacheco came to grief on the coast of Sumatra.
However, while we'll never know for sure, the question is still worth asking.