That makes a lot of sense! My address tends to be very neat on the cards that I don’t see a marking on, and the one where the stamp is clearest has a misspelling on my street name - so perhaps it had to go through twice?
I wouldn’t mind a tour of these places either, I’m always fascinated by how these rather ‘mundane’ (to most!) things work 
Wow! So I’m almost certainly that it has changed a fair bit since I last looked at these markings back during the pandemic. I thought that most of my cards back then had letter facility markings of one kind or another…and that they were from all over the place in Oz too. Not just my local letter facility (in Sydney). I even had cards coming from Europe. Entering Oz in Perth (PMC) and then coming across to Canberra.
But I just took the top thirty cards off my incoming pile and of those, only 8 had mail centre markings on them, and they are ALL from SWLF.
So I have no idea now why some do come through the letter facilities and some don’t (or at least if they do, they don’t get graffiti in the process).
Of the 8 that do have SWLF markings, six of them have been stamped directly over my address, making it very hard to decipher! Good job Oz Post. Why not make a hard job harder? 