I think typing yourself is not as easy as it seems, for several reasons:
First of all, a lot of people have been 'programmed' to play a role and are not acting according to their true type. Especially the influence of traditional gender roles messes things up. It's like Rick DeLong said in one of his articles: if you have not had the experience of duality when growing up, it will be difficult to find your dual. Perhaps you'll adapt and learn to play a role instead of being yourself.
Second, understanding the functions, and especially how these fit in Model A is not easy to understand. It takes time to understand the nuances of a function depending on its position in Model A. E.g. take a person that would be seen by his environment as a know-it-all. At first sight, what type are we dealing with here? With an ENTj, who does know it all and knows how to put his knowledge to good use (leading Te), or an ENFp who communicates his trivial knowledge as a means of impressing people (HA Te)?
And finally, descriptions of the functions, which sometimes are written in such a way that they are not falsifiable. E.g. according to wikisocion:
1. An ENFps creative function is Fi. The ENFp uses that function to connect to other people, or to distance themselves in case a threat is perceived:
IEEs are naturally sensitive to mood, atmosphere, and feelings. They rarely say or do anything that would worsen people's feelings, preferring instead to distance themselves from people and social situations that produce negative feelings. IEEs are naturally skilled at regulating the degree of emotional intimacy between people, which can mean being businesslike (yet polite) as well as warm and inviting.
2. An ISFp has Fe a creative function, which again is used to regulate the emotional distance to other people:
A positive emotional atmosphere is essential to their sense of well being and inner peace, and they either try to create that atmosphere by directly influencing their surrounding, or by simply removing themselves from the situation or people that in their view is the cause of a negative emotional environment.
3. An ENTp POLR is Fi:
Hide their personal sentiments whenever possible to avoid public examination of their feelings.
Now what I think, is that basically the exact same outward behavior is explained by three different manifestations in Model A. So if I'm warm and welcoming, am I Fi, Fe or Ti? All three are possible with these descritions that fall short. This creates a sort of Forer-effect in the Socionic description. This is what makes it difficult for people to decide on their type. More accurate and falsifiable descriptions are needed, and I think that is possible: a lot of stuff needs to be removed from function descriptions, and new stuff needs to be added in order to make it falsifiable. I already said Socionics is a complex theory, and the contradictions in what has been written about it actually makes matters even more complex. No wonder people have trouble finding their type.