This is how the quote tag works in discourse, so after the comma it’s expecting post, topic, and username. If your put something else, it’s not expected to work.
[quote="Alistair Young, post:1, topic:336217, username:avatar"]
Sometimes it’s possible to track down the correct post to attribute, but others it’s not. If you have the id of the post it’s referring to you could do a lookup and get the info.