How did “classic” and “classical” come to mean “historic”?

Solution 1:

Here's a shot at it, not sure if this is accurate but is logical.

Two definitions of the word can combine to form this meaning of Historic.

The first is

of the first or highest quality, class, or rank

The second is

serving as a standard, model, or guide.

I would say, the classic model is also the highest quality model. You can't know the classic model unless it is in the past. Thus, the usage of the word describes something of high quality, in the past.

A classic model for economic growth would be one that is proven to work because of its high quality, It is possible that the fact that it has taken place in the past serves its base for being an historical word.

Possibly.

These and other definitions of classic: dictionary.reference.com/browse/classic?s=t

Solution 2:

Historically important usually has some values to the place or item in place. Values as in something to do with its history and it being old.

Definition of classical

adjective

- relating to ancient Greek or Latin literature, art, or culture:

Definition of classic

adjective

- judged over a period of time to be of the highest quality and outstanding of its kind: 
  a classic novel a classic car

noun

- work of art of recognized and established value: his books have become classics
- garment of a simple, elegant, and long-lasting style.
- thing which is memorable and a very good example of its kind: he’s hoping that
  tomorrow’s game will be a classic.

References:

http://oxforddictionaries.com/definition/english/classical
http://oxforddictionaries.com/definition/english/classic
http://www.merriam-webster.com/dictionary/classic
http://www.merriam-webster.com/dictionary/classical