Do Australian Rola speakers have a date code as part of their markings? I'm looking at one now marked 434/15; obviously the 15 means 15 ohms, but does 434 tell the date?

Going by various articles on speaker dating, if they followed the EIA coding standard, I'm guessing week 34 of 1954. I gather the EIA date code changed to 4 digits around 1961, so if it were 1964 I'd expect it to be 6434.

Does 1954 seem to suit the application?

I don't think so, it's a Rola C8MX with a big ferrite magnet. I thought perhaps 1964. Not 70s of course, by then they were Plessey.

Model 8MX is detailed in this February 1965 catalog: http://www.amvcnsw.com.au/austin1800/Service_Manuals/RolaLoudSpeaker.pdf

It seems the X indicates twin cone. It mentions that the C prefix indicates the "latest" barium ferrite magnet, so that date code may be 1964.

It probably is 1964, then. Elsewhere in Tech Talk there's a 1959 Kriesler with a Rola speaker marked "59" before the impedance code, suggesting that is indeed where they put the date code.

Thanks for the lead on the catalogue, that'll be useful when old speakers turn up. I've got the 1971 Plessey Loudspeaker catalogue, it will be interesting comparing the two.

I have a Rola 12PX it has 1961 stamped on the rim and 30/15 on one of the radial arms near the terminals.
I'm guessing it's 15 ohm but don't know what the 30 indicates.
It is twin cone unit, it is marked 12PX00 on the magnet.
Looking at the PDF in link from GTC it shows that it has an F30 diaphragm, may that's what the 30 indicates.

There are a few Rola documents on Kev's site that my assist with the codes.

https://www.kevinchant.com/general-information.html