It's amazing how difficult if not impossible it is to contact Adobe per country individually!!
Makes one really, really want to not need to use Adobe products.. Why is this? Bureaucracy?
We use Lightroom 3.
We also use OS X 10.6.8 - we have part of our hardware that we need to stay compatible with - so that's why we don't upgrade all our systems. We're looking into multiboot but that's not ready yet.
To stay compatible with 10.6.8 we would need to upgrade to LR 4. - At the moment of writing this options doesn't exist anymore.
We also have a second system running Mavericks. So there we could upgrade to LR 5.
If today I buy an upgrade from LR 3 to LR 5, will I be able to download AND use LR 4 too?
Thank you for answering this question.
LR4 is no longer available from Adobe, regardless of whether or not you upgrade to LR5, so if you really wanted it then you'd have to try and buy it elsewhere (you might find it at another retailer going cheap) in addition to purchasing the LR5 upgrade for your newer Mavericks machine. (Note also that if you start using a catalogue in LR5, it won't be backwards compatible with LR4, so if you wanted to share a catalogue between machines running different versions of LR then that won't work.)
Sorry, but really I think the answer to your question is "no".