24 months is a very, very long time for a milk chocolate shelf life.  Bulk chocolate mfrs will put long shelf lives on their chocolate that they sell, well, because it's in their financial interest to do so (inventory and all).  Most of them have not done extensive shelf life testing on their bulk chocolates.   While you may find a milk chocolate that is still edible at 24 months (and quite possibly even good, depending on how robust the packaging is, which has more to do with gas permittivity than light, assuming opaque pacakging), I'd absolutely argue that it's the not the norm or even realistic for most products.

Given that shelf life in pure chocolate will always be a sensory, not a food safety, item - it's important to note that sensory is in the eye of the beholder, and there are few folks trained in sensory evaluation.  Many folks believe they are excellent tasters, when in fact they're quite terrible at it.  If an untrained individual who is poor at self evaluation (but believes they are adept) is conducting the sensory evaluation, they could quite easily come to a conclusion that a products sensory attributes are acceptable long past the time when they are, in fact, not...

BartBasi:
I have agree with Sebastian.  We start with the closest date on anything, our concern is maintaining top quality.  After we produce our first batch we hold that back; keep that in our case and we eat them daily.  Generally we quickly find after 2-3 weeks the flavor has had a noticable drop and that's the date we put on it for ourselves.  From a safety standpoint we measure water movement to get an idea about bacterial growth.  The projections from that let us know it's reasonable that our chocolate is good for months (if not years) - but that's meaningless to us because we can tell a drop in quality much sooner. So the short answer is we eat it. YMMV

Thanks BartBasi!

MJ, thank you for your response. The question arose out of a marketing meeting, not a production group. It was hypothetical, not procedural. I always feel it is in the best interest of all to extend questions beyond the inner circle to avoid confirmation bias.

Must say I was a bit surprised to read this question posted from someone whose company Davis Chocolate is manufacturing products, private labelling, co-packing and I assume selling in interstate commerce? 

You business model puts you firmly in the category of a commercial concern that is required to be registered at FDA as a 'Food facility' and also required to fully observe and understand the CFR (Code of Federal regulations) that apply to chocolate and related food stuffs. 

To answer your question checking the FDA website will help with the questions you posed.  As a starter the following is taken directly from the FDA site and might help?

"With the exception of infant formula, the laws that the Food and Drug Administration (FDA) administers do not preclude the sale of food that is past the expiration date indicated on the label. FDA does not require food firms to place "expired by", "use by" or "best before" dates on food products. This information is entirely at the discretion of the manufacturer.

"A principle of U.S. food law is that foods in U.S. commerce must be wholesome and fit for consumption. A "best by", "use by" or expiration date does not relieve a firm from this obligation. A product that is dangerous to consumers would be subject to potential action by FDA to remove it from commerce regardless of any date printed on a label."

Some other thoughts....
Using any 'expired' or 'aged out' materials in a manufactured product is very poor manufacturing practice. "Good manufacturing practice" for both an artisan confectioner or a large commercial operation would require a bill of materials with the specifications and traceability / lot number of items like 'dried milk powder' recorded including expiry dating.  That said, in fact dried milk powder (DMP) is actually long lasting if stored dry and dark, it has been stored for years as a food for emergency relief use, or as part of the European commodity price protection program.  In the 1980's the  European intervention stores (huge warehouses) were full of sacks of DMP.  Personally, I'd use dried milk or milk crumb well in date for making milk chocolate.  Once all incorporated as final compound the combination of DMP, sugar and chocolate liquor yields a aW (water activity) usually well below 0.65 and milk chocolate is a shelf stable food from a microbiological standpoint,  that's without considering the changes in temper / sensory qualities that with occur during storage. 

By convention a product's 'shelf life' starts the day it completes manufacturing and is 'product released' from the production area / factory.    Your formulated product.... Milk chocolate I'm assuming in your case? should have a shelf life assigned from your experience of prior batches held and examined for quality after X months (bloom / temper other issues?)  Alternatively, a conservative short dated 'Use by" set and perhaps updated using results of a 'real time' stability study of a sample of your current production (hold back sample) could be used. (Personally I'd not be a fan of this approach.)      

Typically well made quality milk chocolate has a shelf life assigned by an experienced manufacturer of around 18 - 24 months from date of manufacture when stored at 68F in impermeable packaging protected from light.  Shelf life is an issue for bulk purchasing for small companies,  if I buy in bulk to get decent prices and then hold in stock, I'd typically ask for the product production dating when ordering 500lb lots and would reject short dated goods.  
    



MJ

I have agree with Sebastian.  We start with the closest date on anything, our concern is maintaining top quality.  After we produce our first batch we hold that back; keep that in our case and we eat them daily.  Generally we quickly find after 2-3 weeks the flavor has had a noticable drop and that's the date we put on it for ourselves.  From a safety standpoint we measure water movement to get an idea about bacterial growth.  The projections from that let us know it's reasonable that our chocolate is good for months (if not years) - but that's meaningless to us because we can tell a drop in quality much sooner.

So the short answer is we eat it.

YMMV

Thanks Sebastian

That's a bit of a complicated question.  It's a combination of how you store and process your raw materials,  how you store your finished goods, and ultimately what the sensory on them looks like at a given date (and what you consider to be acceptable for sensory)...

How do you determine Best By vs Sell By vs Expires on multi-ingredient products? For example, if the milk powder expires on a specific date, does the chocolate bar also expire on that date? And what defines "Best By"?

Beth