What is the appropriate usage of example names?

Question

Sometimes it is the case that fake or example names will be used in place of actual names for purposes of explaining something.

For example:

田中さんの主張には、その点において疑問があります。

I have a question about one of Mr. Tanaka's points.

As a name, "Tanaka" is not so important, it is just a filler in this case.

I noticed that sometimes instead of a name, letters can be used like A, B, C..

Aさんの主張には、その点において疑問があります。

I have a question about one of Mr. A's points.

However, is it appropriate in Japanese to use "Aさん" here especially if "Bさん" doesn't exist? When is it appropriate to use an actual name like "田中さん" or a letter "Aさん"? Or is there not any distinction made in Japanese?

EDIT: What context best suits these naming conventions? Can "A,B,C" be used in the context of literature or is it only limited to Mathematics? In the example above why might "Tanaka" be a better fit compared to "A,B,C"?

Answer 1

There are different methods to use in different contexts. For form samples, they tend to use the institution name in place of a family name and stereotypical names such as 太郎, 花子 for the given name.

三井 太郎
河合 花子
○○大 太郎

In real estate contractions, traditional variable names are used. Cf.

甲は乙に対して、...

In mathematical contexts, it is natural to use roman alphabets.

A は B が出発した10分後に出発した。

In mass media, to make the person annonymous, an initial may be used. Cf.

Aさん(27)の絞殺死体が発見された。

Answer 2

In most sentences, A,B,C... would work well. It's okay to use in casual essays / blog/news articles too. Use 甲乙丙丁 only for contracts and laws.

In case you want to specify sex, use some suffixes such like A子 for female, B男 for male.