Bikes were old, of prewar make.

Johnson13Do you agree?

No, make is uncountable.

Johnson13....A sentence by a Nobel laureate: Bikes were old, of prewar make.
I think an indefinite article should be placed before "prewar", because "make" is not an uncountable noun.
Do you agree? I agree that "make" is countable, but that doesn't me

Does it mean sometimes after OF a usually countable noun can become uncountable?

Here's a sentence:

Her verse always gravitated to the vernacular, to the idiom of folk song.

Is this sentence OK for the same reason?

Here's a sentence:

The elements of howl, however, are quite audible in other poems of the period and later.

I know four dictionaries with (non-)count labels, and they all include HOWL as countable, so do you think in the above sentence an S is needed?

Johnson13the idiom of folk song. … the elements of howl

These are not everyday phrases, so it’s difficult for me to judge.

Johnson13Does it mean sometimes after OF a usually countable noun can become uncountable?

I think you're on the right track.

After of (and other prepositions) articles are sometimes dropped before singular nouns. This may make it look like the noun has 'become uncountable', but it doesn't matter whether the noun is countable or not. The whole

Thanks.

But when I typed the sentences from my paperback, I followed all the cases.

howl - in the book does not have a capital H.

Johnson13howl - in the book does not have a capital H.

Maybe that's the way the poet originally titled it. I don't know the answer to that one.