I don't know since you'll probably get a new calculator. What I'd advise, if it is doable, is to go in stores and look for calculators in the old packaging. If you find one, you're sure it'll support Ndless. But with orders, you can get anything.

edit3 don't read those edits, I messed up and edited this post instead of that one

edit weird, I tried in another folder that contains space, it works like a charm
edit2 One of the subfolders it is in has a quote ' in its name, could this be the problem ?

I'm sorry I'm not sure what you were referring to in you edits. Are suggesting you have one of the newer models and it worked for you?

I think those edits were supposed to be in http://ourl.ca/20256/369898.

Theoretically how old of a model should I be looking for? I was interested in that one due to a backlight and rechargeable battery.

There are definitely calcs of this model that work, you just need one that's produced earlier. I can't remember when they changed the hardware, though.

A model from 2011 should work, as long as the previous owner didn't slap a copy of 3.6 on it.

I have no clue about 2012 models, some might work, but I am unsure about how old they have to be. Also I don't remember how the new packages look like.

Just to confirm what LDStudios said: I got my newer CX in May 2013 and it is fine, but I know someone who got his in June 2013 and it has hardware revision J.