No because Unique/Named creatures are not the "average example"
As @Crazjtk correctly pointed out the examples you gave, Titivilus, Yan-C-Bin, Kiril Stoyanovich, and Ahmaergo, are not unique creatures but rather exemplary examples of a particular kind of creature. This is easy to see in the cases of Kiril Stoyanovich and Ahmaergo who are a werewolf and a Dwarf respectively.
It is harder to tell in the cases of Titivilus and Yan-C-Bin however because we do not know what the "average example" of their type of creature is. We don't actually need to know what an average Titivilus type creature is just that Titivilus is not average. I believe that we can conclude that any named creature is not the average-form of a creature type. If a player encountered Griphook the goblin, whose stats were exactly those of a standard goblin, the player could not shapechange into Griphook only an average goblin. That the two are identical is incedental.
We do not know from the books how the DM defined the origin and history of Titivillus. It could be that in your game's universe Titivillus is an average example of his type of creature, be it because others are all like him or because he is unique. Even if that were the case a player could only turn into Titivilus's type of creature not Titivillus.
Since there is no provided stat block for an average Titivilus-type-creature it becomes up to the DM to define one. A kindly DM might determine that Titivilus is entirely representative of his kind while a DM that resents being made to make up a new monster might declare Titivilus to be nothing more than a particularly empowered Lemure. This isn't a danger with creatures that have defined "average" forms but whenever the average form is not provided only the DMs imagination can fill in the blank.