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You wrote:
The term proto-Protestants has been in use now for quite a long time to describe religious movements sharing the beliefs very similar or even identical (as far as key issues are concerned) to those professed by Protestants of the 16the century. 

I was unable to find this definition online can you post a link.

Continued:
There clearly is a group of such movements, including the Waldensians, the Lollards, the Hussites, but also in the earlier centuries, the Vigilantians, the Aerians, the Helvidians, the Jovinians, whose views were identical to those of many Protestants.

I don't know that it is all that clear. Identical? Aerians insisted that the observance of Easter was a Jewish superstition and they fasted on Sundays. Not very Protestant. The Vigilantians argued against the veneration of relics, the sending of alms to Jerusalem, the rejection of earthly goods and the attribution of special virtue to the unmarried state, especially in the case of the clergy. No mention of the Bible, no mention of justification, nothing else Protestant. All that is known about Helvidius is that he did not believe in the Virgin Mary.  That doesn't exactly make him a Protestant. Identical is laughable - there is no evidence to back up such an assertion. Wikipedia is not about truth, it is for fact that can be cited with recognized secondary sources of evidence.

You went on:
This becomes even more obvious when we consider the fact, that the Waldensians, the Lollards and the Hussites joined the Reformation and often mixed with various Protestant groups. The Waldensian Church, still existing in Italy, is considered a Protestant group and not a sect, as User:Secisek tries to imply. This is because all key beliefs the Waldensians have professed since the 12th century are common to most Protestant groups and are different from those professed by sects considered heretical by both the Catholics and the Protestants.

Whoa, I did not imply they were a sect, I wrote that they were. I intended no offense with that word. The Waldensians were a sect, and they revised their doctrine at the Reformation to conform to the new Protestant thinking. This is taken from the Waldensian's article:

""In 1532 they met with German and Swiss Protestants and ultimately adapted their beliefs to those of the Reformed Church. Moreover, the Waldensian absorption into Protestantism led to their transformation from a sect on the edge of Catholicism that shared many Catholic beliefs into a Protestant church adhering to the theology of John Calvin, which differed much from the beliefs of Peter Waldo. From that moment the Church became the Italian branch of Reformed churches.""

This contradict your assertion:
The Waldensians have never altered their key beliefs, they are considered Protestants and still they had existed for over 3 centuries before the proper Protestants and the Reformation. Many scholars have used the term proto-Protestants in their articles, although there do exist historians who argue that the term should not be in use for various reasons.

The fact is, they have altered their key beliefs - that is what made them Protestant.

The problem is, however, that the Catholic historians often argue against the term to show that Protestants appeared only in the 16th century, while before them, there was just one Church of Christs and many small sects. For this reason even Waldensians, now considered a part of the Protestant Church even by the Church of Rome, are called a sect by Catholic historians. This dychotomy is absurd, as it implies that the Waldensians were at first a sect and then a Protestant group, while they have never changed their beliefs in the course of History. If the Waldensians are Protestants now, and they maintain the same views they professed in the late 12th century it means, that they have always been Protestants, even when the term had not been in use.

They have not maintained the same views, read the Waldensian article. They were still taking Roman Catholic Eucharist until the time of the Reformation, with the belief that the validity of the sacraments depends on the worthiness of the priest performing them. Seven sacrament is not very Protsestant.  

I am not a Roman Catholic, nor do I care what Roman Catholic historians argue, although I am sure RC historians would at least acknowledge the existance of the Orthodox and Oriental Churches rather then maintain that there was ""just one Church"". The facts are quite clear - Protestants appeared in the 16th century for a variety of historical and cultural reasons that existed at that moment in history. They could not have appeared before that moment and it mental gerrymandering or wishful thinking to believe otherwise. I will be happy to discuss this further, but it seem that the