More than Five?
 

In the text of LOTR, Saruman mentions 'the rods of the Five Wizards' and among Tolkien readers it is generally accepted that there were only five of that Order. But after reading this passage from Unfinished Tales I consider it possible that there were more.

So the five whom we know were only the chiefs among those who came to the North of Middle-earth. That implies that there were more Wizards in the North, and even more in other parts of Middle Earth, the ones 'off the map' provided in the book. And why not? It makes sense that the Valar would send more than a measly five messengers, considering the sheer size of Middle Earth.

What say you?

Actually, it's even more interesting: not to other parts of Middle-Earth, but the quote you provided implies that there were more sent to the North, and among them the chiefs was five. From other things that are said about Wizards, Valar certainly had main interest in supporting the resistance in the NW Middle-Earth, as there the resistance against Sauron was the greatest, so maybe it is even more probable that more Wizards were sent to the North than that there were even any sent, let's say, to Harad (though I'd find even that logical, as "support of resistance" would be surely helpful even there as "infiltrators" - nevertheless, the Wizards were forbidden to use too much of their power, so they surely wouldn't be that efficient). But anyway, as the quote speaks about those sent to North as a group, it could be concluded that there was another group in contrast to this one, and that was sent elsewhere.

One personal interpretation here. It is playing with the text a little, but when I was making an RPG setting for late 3rd-Age Middle-Earth and one of my players chose to be a wizard (though an Elf), we used the hazy language of this text to our advantage and, though he was simply an Elf from Middle-Earth, of course with no particular contact with Valar or anything, we in fact placed his character under the group labeled "Istari" as one of these "other" Wizards in the North. What allowed us to make this move: the text does not necessarily say that all the Wizards had to come from Valinor, and it does not say explicitely in which way they were "called" for their assignment. It was balancing on the edge, yet we interpretated it the way that this wizard character, having a vocation from Valar - but not any "physical" one, rather a kind of "inspiration", he probably did not even consciously know he has this assignment from Valar - would be, at least in the eyes of the historians several hundred years later, labeled as one of the Istari.

I wanted to use this illustration to show that the borders could be somewhat hazy and that not all is gold that glitters, respectively, in this case rather not all that is gold has to glitter.

Back to something concerning the topic in general: There are other quotes, however, that deny that there will be any other Wizards than the Five. Nevertheless, I consider what you posted an important piece of evidence that should be taken into account and not simply dispatched.

I've discussed in other places about this and the conclusion we always came to was that there were only 5 wizards and no more.

Now, for a nice analysis you can read http://www.barrowdowns.com/faq_istari.php

Now, what I really like to draw your attention to is the difference between ealier and latter texts:

Unpublished essay on Istari from 1954 (later published in the UT):
Letter from 1956:
Another letter from 1957:
Also from 1972:

All in all, I personally go with 5, because in later works Tolkien always spoke this way. On the other hand you have an unpublished essay from 1954...which I don't really believe.

The Might, one can argue that the 'five wizards' mentioned in those later letters only refers to the five that were in the group sent to the North of Middle-earth. When Saruman said 'the Five Wizards' he could have been referring only to the five members of his own group.

Now, it is possible that others remained in Valinor, but reading through Sharkû's essay linked above I rather tend to believe that the Heren Istarion was, as Sharkû very nicely shows, only an ad hoc organization formed only to help the free people of M-e get rid of Sauron, and that the order mentioned in the quote from the UT actually is that of the Ainur.

Again, I highly recommend reading the essay. The idea that other groups of Ainur under the leadership of others then Curunir made their way to other regions, for example the south of M-e is unlikely as showed in the essay. Again unlikely, but not impossible.
Still, I don't see why we should think there were any others as long as others were never mentioned.

It's also possible to read it that the title 'Wizard' was applied only to the five Chiefs (Saruman refers to "THE Five Wizards"), but that there were other emissaries who were of lesser degree and didn't merit the title.

One thinks immediately of Gwaihir, for instance. And there is also the 'near-Maia' Glorfindel.

In one place actually Tolkien did wonder if Glorfindel was a wizard at one point.