Does «bistec de res» differ from «bistec» or is the former just redundant?

Question

I have seen a few signs and menus in Mexico City that say "bistec de res". I understand this, though, to mean "beef steak of beef". The de res seems totally unnecessary to me, whose first language is English, and I am curious why it is included.

According to Wiktionary, bistec comes, as it appears, from the English beef steak.

According to Spanish Dict it means

(culinary) a. steak b. beefsteak

The first definition, I suppose, is vague enough to allow for the clarification of de res to be helpful. Can bistec refer to non-beef steaks?

I was surprised to learn that res doesn't necessarily mean beef:

1. (animal) a. livestock b. beast c. cattle
2. (culinary) (Latin America) a. beef
3. (culinary) (Mexico) a. steak

Bistec de res is obviously a culinary reference, so we can ignore the first part of the definition. The Mexico specific part of the definition actually surprises me more, because it means the de res doesn't add anything to bistec, as it would if the latter no longer carried the connotation of beef: the (beef) steak of steak.

Perhaps it is that bistec still means beef but but necessarily steak (and in fact often you receive bistec finely chopped, no longer in steak form) and the res clarifies the form rather than the animal?

Does bistec de res mean anything different than bistec, either by definition or nuance?

Possibilities:

1. Bistec is a generic word for steak; de res clarifies the animal.
2. Bistec is a generic word for beef; de res clarifies the form.
3. This repeated construction is the erroneous product of uninformed writers.

Answer 1

In my mental dictionary, a bistec is any kind of big/thick piece of meat (of course this is not representative, but I would say many other native speakers see the word in the same way). If we go to DLE, it says:

Filete de carne de vacuno

Then, if we go to res on DLE, it says:

Animal cuadrúpedo de ciertas especies domésticas, como del ganado vacuno, lanar, etc., o de los salvajes, como venados, jabalíes, etc.

Meaning that a res is not exclusively beef, as you have noted/noticed. In my mental dictionary (again), a res would tend to be beef, and this is the case in Colombia, Ecuador, El Salvador, Guatemala and Mexico, where it means (again according to DLE):

Animal vacuno.

So all this basically depends on how accurate or even grammar-nazi you want to be. For some people they will be redundant, and for some others it won't.

Answer 2

I am from Mexico. In here, 'bistec de res' means that the meat comes from a cow. 'Res' means cow.

We also have bistec of pork, and so we use it to distinguish what kind of animal the meat comes from.

Answer 3

When you go so much in details, dictionaries from one language to another could be worthless, try finding a definition in that language:

bistec: Un filete, bistec, bisté o bife es cualquier corte de carne roja que haya sido cortada en forma de filete para el consumo humano.

and Res means beef here.

But you may want to know additional information, what part of the cow it is from, what quality of that part, how it’s been prepared and cooked.