True chocolate, made with cocoa butter, especially of the non-milk variety has a very long shelf life when stored in dry, cool conditions. The fact that the shape is a chip rather than a bar or disc or callet is not really relevant, except for the total surface area on which blooming can occur.
Chocolate is very, very dry, which discourages mold, bacteria, or other micro-flora or micro-fauna from growing, not even counting the preserving effect of theobromine and other alkali in the chocolate.
It also resists rancidity very well. Stored properly, it can last for many years safely.
Many brands of chocolate chips are not true chocolate, because the manufacturer may have used less expensive fats than cocoa butter, which do not have such excellent storage properties. Assuming you have a quality chocolate chip made from real chocolate, the issues you may find include:
- Sugar bloom, where the sugar comes to the surface due to moisture dissolving it and then leaving it on the surface when it evaporates
- Fat bloom, where the cocoa butter separates out onto the surface for reasons not thoroughly understood
- The chocolate can lose its temper from warming and cooling cycles, if it gets too warm; this will change its texture to softer, more gritty, and less pleasant
- The cocoa butter could go rancid (which I have never experienced)
The first three are aesthetic and cosmetic issues, but the chocolate can still be used in recipes or melted down and re-tempered.
Having it go rancid would be cause to throw it out--but chocolate is very hardy, and resists rancidity--so if it tastes fine, it is still usable.
After two years, you are quite likely to have experienced bloom. The chips will look like they have a white coating, and may feel gritty. While this makes it less pleasant to eat out of hand or in applications where it won't be melted down, it will still perform well in recipes where it is melted.
They are certainly safe to eat (again, assuming real chocolate, and no rancidity), but they may not have the same pleasant texture and crispness that you would expect. This is why manufacturer's give them a best by date.
Note: you can tell whether they are real chocolate by the ingredient list (at least in the US, and other places with comparable labeling laws). Real chocolate will consist of:
- Cocoa solids, cocoa, cocoa mass, cocoa butter, cocoa nib, or chocolate liqueur (all words indicating products of the cocoa bean)
- Flavoring (such as vanilla or salt)
- Perhaps lecithin as an emulsifier
Signs that the product is not real chocolate include other ingredients, especially other fats in lieu of cocoa butter (which is comparatively expensive, and marketable to the cosmetics industry).
Milk chocolate, which also contains milk solids and milk fat will not last as long, but still probably has a shelf life measured in years when stored under proper (cool, dry) conditions.
White chocolate chips do not have the additional preservative effects of the cocoa solids and their alkali, and also have dairy solids and possibly milk fat, so they have the shortest shelf life of all. It also tends to pick up off flavors if not in a perfectly sealed, air tight container. White chocolate, I would not keep more than year or so.
Of course, chips that are made from other ingredients than true chocolate are going to have a shelf life based on their ingredients, but I cannot speak to that, and anyway, in my mind, they are not worth storing.
Why does dark chocolate turn white after being in cold for some time?