Past passive voice, with or without “был”

Question

Is there any difference in meaning in the past passive voice used with or without "был"?

Москва основана в 1147 году.

Москва была основана в 1147 году.

Answer 1

Of course. There is no difference in your case, however, the variant without "был" refers to the present state. Nowadays you cannot say "Советский Союз образован в 1922" because Soviet Union does not exist anymore. Moscow does, so you can use both.

Answer 2

The easiest analogy is as follows:

• Moscow was founded in 1147. (w/o быть)
• Moscow has been founded in 1147. (w быть)