Comparative adjectives in general, stand-alone use (meaning slightly)

Can a comparative adjective mean 'slightly', 'kind of', without actually referring to another term?

The understanding of longer texts is necessary for an C1 certificate.

Meaning that you need to understand moderatly long texts. Not in the meaning of writing longer texts than before.

I prefer the darker coffee roasts.

Meaning that you don't like either very strong or very delicate roasts, not meaning that you like coffee stronger then the one you are drinking now.

His new novel can be bought at (the) better book shop(s).

The novel can not be found in every store, but in many.

I feel the second example is correctly used while the third one is a (terrible) contamination from my native language. What about the first example?

Solution 1:

The use of a comparative adjective without reference to another term is very common in American English. It indicates a comparison with either the average of the class being discussed or a known range of that class.

The understanding of longer [than average] texts is necessary for an C1 certificate.

or

The understanding of longer [than many of the others in this group] texts is necessary for an C1 certificate.

There is no difficulty for native speakers with the third example.

His new novel can be bought at better [than average] book shops.

or

His new novel can be bought at the better book shops [in this city].