I read 日本語の助詞(情報構造） and from what I understand it says:
What comes before は is old information and after it it's new information. (This makes sense to me).
What comes before が is new information (this makes sense to me) and after it it's old information (This does not make sense to me though).
So I tought of a conversation in my head.
My parents call me at the cellphone while I am in a bar with some friends.
My friends ask me what's wrong and I answer: お祖母さんが死んだ。
I am not sure if this is correct to be honest, but this is how I think it would go.
My reasoning is that me and my parents already have a mental referent for お祖母さん and we assume she existed, therefore old information は. My friends do not know that I have a お婆さん so she is new information therefore が, but the fact that she died is new information too.
So from what I understand since は is the only old information what comes is all new information right?
Also by reading:
It makes sense that you separate the old info from the rest and you add new info.
Can someone explain to me if I am wrong? From what I understand the only old information is marked by は (and も), while the new information is marked by all the other particles (がをにで and も included).