1. I'm talking about the car in front of my house which someone parked without my permission.
2. The rays from the sun from which plants make oxygen, could be harmful to the skin if they penetrate the ozone layer too much.
3. The movie was funny, about which you told me before.
4. Our circumstances are beyond our control, which eventually led us to go separate ways.

(There is no comma in 1 and 2, but there is a comma in 3 and 4)

Q1) Are both sentences 1 and 2 correct English or acceptable English even without a comma that should be inserted before "which" and "from which" ?

Q2) As for sentences 1 and 2, is it common that even a native English speaker write sentences 1 and 2, omitting a comma that should be put before "which" and "from which"?

Q3) Are both sentences 3 and 4 correct English or acceptable English even with a comma inserted before "about which" and "which" ?

Q4) As for sentences 3 and 4, is it common that even a native English speaker write sentences 3 and 4, using a comma to set off "about which" and "which"?

Q5) As for 1, even without a comma, does "which" refer back to "the car"?

Q6) As for 2, even without a comma, does "which" refer back to "The rays"?

Q7) As for 3, even with a comma, does "which" refer back to "The movie" ?

Q8) As for 4, even with a comma, does "which" refer back to "Our circumstances" ?

Q9) In short, is context what makes "which" seen as referring back to, not the comma? and normally, are native English speakers not focused on the use of commas?