I am just trying to get a rough idea of how long a pressure canned soup can last. We made turkey soup with thanksgiving leftovers, which we canned. I have it dated from 10-28-2012, so it's a little less than 5 months old. I followed the pressure canner instructions for meat products (10psi for 25 minutes). I opened the jar and it smells good and tastes ok. I just can't find any reference for what shelf life to expect.
While they are almost certainly very conservative (and with good reason), the FDA recommends that you plan on using home canned goods within one year. They do not give shelf-life guidelines other than this.
I could not find truly authoritative sources (FDA, a major university extension center) that provided more detail. Less authoritative sources make various claims, on the order of several years, but I will not quote them or link them here.
A five month old jar is certainly well within year that the FDA guidelines suggest, assuming you followed good canning practices. The fact that you took the trouble to date the jar is a good indicator of your diligence.
If you processed the soup for 25 minutes, you have under processed it, according to the USDA guidelines. The USDA guidelines call for processing soup (vegetable, meat, bean-based) for 60 minutes for pints and 75 minutes for quarts; they call for processing soup that contains seafood for 100 minutes.
The 20/25 minutes processing time is only for meat stock, which is liquid. (Remember that density has quite an effect on processing times.)
See section 4-18 of the USDA Complete Guide to Home Canning Guide 4: Selecting, Preparing, and Canning Vegetables and Vegetable Products: http://nchfp.uga.edu/publications/usda/GUIDE%204%20Home%20Can.pdf
See page 5-7 of the USDA Complete Guide to Home Canning Guide 5: Preparing and Canning Poultry, Red Meats, and Seafoods: http://nchfp.uga.edu/publications/usda/GUIDE%205%20Home%20Can.pdf