I bought 2 bottles of ILFOSOL 3 developer some time ago and I can't tell how old they are. There doesn't seem to be a date of manufacture or expiration date. There is just a batch number. One of the bottles has been opened and I used some of it. I will toss that one. I would like to use the other unopened one if it is under the 18-month shelf life. But, how long is ILFOSOL 3 really good for? Has this been successfully used after the 18-month official shelf life? It has been kept unopened in a cool dry basement the whole time.
Sounds like your real question is: Can I use this developer?
The answer, of course, is a question: How important are the images to you?
If this film is critical and the loss of any images meaningful, then go get new developer; the stuff isn't that expensive.
If, however, you are okay with the risk, then read on.
Are there precipitates in the liquid or crystals growing in the bottle? If so, chuck it.
How's the color and odor as compared to what you know as fresh? If it is significantly off, chuck it.
If, however, it's color and odor looks and smells new and there are no precipitates or crystals, then conduct a test.
Expose a scene with a good range and then snip those few frames and the leader and load into the tank in the dark. Process normally using the developer. Your film leader should be a deep, opaque black while your scene should develop as you expect it to. Frame numbers should come out along with any other edge markings.
If the leader is not opaque or something looks off about the test images, then consider your developer junk and chuck it. Conversely, if all looks good, then load up your full developed role and process.
As an aside, one of my favorite films is PanF+ in DDX. But, PanF likes to be developed immediately and DDX doesn't have the longest shelf life in the world. When I shot a lot, this mattered little. Now that I'm shooting a bit less, I keep a bottle of Rodinal on hand since it will probably outlive me and use that for one off roles of PanF+ or other films. If I'm looking to develop in something else, I'll toss the exposed rolls into an air tight container filled with far too many silica packets and store in the fridge. Develop when there's enough rolls to use up a small bottle of DDX or similar or 6 months go by, whatever comes first.
I've never tested for latent image degradation. Also haven't noticed a problem, either.
Place a thimble full in a thimble size bowl. Cut a sliver of film off the tongue. In the light, swish this sliver in the developer. If it blackens, after a few minutes, likely the developer remains active. Also, expired developer is oxidized and turns dark or even black. This is because the chief ingredient is a close cousin of benzene. As the developer oxidizes it reverts to coal tar. Benzene was initially produced from coal.