If it weren’t for VS If it hadn’t been for
Hi!
Recently I’ve come across this expression. The meaning is clear, but I’m puzzled over the following examples:

1. If it weren’t for those quick-thinking bystander, I wouldn’t be alive today
2. If it hadn’t been for the two men who rescued me, I would have drowned.

The situations seem pretty similar to me, but why different conditionals are used? Are there any shades of meaning?
Thank you for your comments and explanations:)

Question

If it weren’t for VS If it hadn’t been for
Hi!
Recently I’ve come across this expression. The meaning is clear, but I’m puzzled over the following examples:

1. If it weren’t for those quick-thinking bystander, I wouldn’t be alive today
2. If it hadn’t been for the two men who rescued me, I would have drowned.

The situations seem pretty similar to me, but why different conditionals are used? Are there any shades of meaning?
Thank you for your comments and explanations:)

Answer

Hi Yana:) 
The first one is unreal situation in present time.
The second is unreal situation in past.
Good luck

Answer

Verb agreement is part of the answer.

Were and it are forms of the verb “to be”.

Have and had are forms of the verb “to have”.

You don’t went to mix the verbs in the same sentence.

Answer

To me, they have the same meaning.

Sometimes “hadn’t been” is said as “had not been” so it can be emphasized to help make a point.

Also, the word weren’t does not sound quite as nice as hadn’t.  Others here might have more academic answers for you.