What is Value-Producing Labour?

The question is the following: which kind of labour "create" values?

If we answer: it is productive labour "creates" value, then this answer is just a tautology.

If we answer: it is labour that produces products and that is embodied in them "creates" value, then this answer is still ambiguous because you do not define what is the product. Can we say circulation workers produce "service products"? Are they labour embodied in such so-called "service products", and eventually, are their labour productive?

The above answers are not satisfying, these answers still have something needed to be defined. 

So we need another criterion to judge what kind of labour "create" values.

For Masako Watanabe (渡辺雅男. Sorry I just found him in Japanese Wiki, but you can translate this Japanese website page into English by Chrome), a Japanese Marxian economist, to evaluate whether the labour creates value, we need to check whether this kind of labour satisfies the principle of fixed input-output ratio. If the answer is yes, then this kind of labour creates value, otherwise, this kind of labour doesn't create values.

I would like to know how do you think about his opinion?

Anyway, here is Watanabe's argument:

First, recall Marx's original text:

Now let us consider merchant's capital. Firstly, the purely commercial operations. It does not take more time to deal with large figures than with small ones. It takes ten times as much time to make 10 purchases at £100 each as it does to make one purchase at £1,000. It takes ten times as much correspondence, paper, and postage, to correspond with 10 small merchants as it does with one large merchant. The clearly defined division of labour in a commercial office, in which one keeps the books, another looks after money matters, a third has charge of correspondence, one buys, another sells, a third travels, etc., saves immense quantities of labour-time, so that the number of workers employed in wholesale commerce are in no way related to the comparative size of the establishment.

Marx: Capital III, Chapter 17. Commercial Profit

Notice that in the last sentence of this paragraph, unproductive labour - commercial labour does not have a fixed input-output ratio. Therefore, Watanabe argues that we should use the principle of fixed I/O ratio to judge whether a kind of labour is productive or not.

Watanabe has a paper on this topic. I know this paper has Chinese and Japanese versions, but I am not sure whether his paper has an English version. Here is the English title of his paper:

The Value theory of Labor and Productive Labor: On the scope of Value-Producing Labour