Alan,
I have quite a bit of experience of this product, and while off the top of my head I can't remember the best before date I'm fairly sure it should last for a minimum of six months. The 64floz container will produce 128 Mocha's (half a fluid ounce per drink), for a hot chocolate a full fluid ounce should be used. If you use the dispensing pump supplied then there is a bit of a problem getting the last dregs from the bottom - the best way is to warm the bottle in a sink of warm water to melt the sauce a bit then poor it out (when warming always leave the top open - I'm reliably informed that the air expansion in the bottle while warming builds pressure in a sealed bottle - and finally opening it results in a chocolate explosion.
I have heard of isolated cases where when used sporadically over a long period mould can develop on the pump shaft inside the bottle - although this could be due to very humid warm cafe environments.
For best length of life you could just use the bottle with the screw top as provided standard, and if you have a big fridge keep it refrigerated to extend the life.
For a more definate answer you could try e-mailing the manufacturer:-
http://www.ghirardelli.com/
I hope this helps, it does make wicked Mocha although a bit sweet for my taste.
Rob
Long forgotton Tech and Coffee Equipment guru.
Twitter: @c0ff33a
As I walk through the valley of the shadow of death I take a look at my life and realise there's none left 'Cause I've been brassing and laughing so long that Even my mamma thinks that my mind is gone