If you do a google search for shortening shelf life you get ALL sorts of responses. Typically you get the manufacturer's response (which I believe is "weighted" to encourage consumers to buy more product, and the "average Jane" response which isn't scientific.
Crisco FAQ says 2 years unopened (assume the newer, non-metal packaging):
Here's a chef column which answers the question (sort-of):
Here's an "average Jane" response from a survival site. (NOTE: The difference in storage of METAL cans and cardboard or plastic is significant. Personally, I haven't seen a metal can of shortening in quite a while.....)
"If you have no particular problem with using it, the culinary fat with the most shelf life as it comes from the store is hydrogenated shortening in its unopened metal or metal lined can. The brand most familiar in the U.S. is probably Crisco (tm), but there are many others. Solid shortening is usually composed of partially hydrogenated vegetable oils, but there are some that also contain animal fats. Some brands will also contain anti-oxidant preservatives as well. All other conditions being equal, those with preservatives will have a longer shelf life than those without. It is not possible to give an exact answer, but it is reasonable to expect an unopened metal can of shortening to have a shelf life of eight to ten years if kept reasonably cool, particularly if it has preservatives in it.
Here is an excellent, well-written, well-researched excerpt from a book, "How Baking Works: Exploring the Fundamentals of Baking Science, By Paula I. Figoni.
This excerpt says that LIQUID
HIGH-RATIO has the longest shelf-life of any shortening product, but cake decorators typically use what this author calls, "high-ratio plastic shortening".
Sweetex with trans-fats recommends a one year shelf life. However, here's a particularly nice thread on CC on the topic. (There are tons of threads online about the shelf life of Sweetex.)