I really debated saying anything about this for a few days as I didn't want to step on anyone's toes.
This was brought to my attention a few years ago (i.e. about 7yrs now), and at that time was/is referenced from engineer's/expert's participating in a world wide passive house design gathering. The conclusion is, at some point in time the "R" value will be basically zero in all foam products. As foam insulation was originally used under ballusted/EPDM or rubber roofs, and these had a 15yr life expectancy, that is all the product was ever needed to last too, as it would be replaced when the roofing was replaced, and at least to that time (7yrs ago) that was still how the industry was rating foam products.The company I worked for at the time, also sold SIP panels made from an outside vendor, but never shared this information with their Clients, even though they also built their own high performance panels that did not use foam.
Like anything, hopefully time has expand the knowledge and duration's, as an example, take when SIP panels first came out, the manufacturers, didn't know ants liked the foam so much, and the ants decimated the foam inside the panels. They found they needed to add a chemical to the foam to keep the ants from infesting and eating it. They also found that "mix" of chemicals was extremely important, as a bad mix lowered the "R", caused the foam to shrink, could also cause shrinking and twisting of panels which required replacement, etc.
I am not saying not to use it, but be aware of it's plus's and minus's. I would definitely use it under concrete floors, against earth, under ballusted/EPDM/TPO/rubber roofs and areas like that. I also am not saying you might not get a long life from the insulation, but only saying the product has been tested at that "R" value for a 15yr life expectancy. Take the "old" asphalt shingles (before fiberglass reinforced) they had an expected life of 10yrs or so, but, I have seen them get upwards of 25yrs to 30yrs. As an fyi, Googling the subject yesterday, I see manufactures claiming everything from 20yrs to 50yrs for their foam products.
However, personally, especially after the information I received, I am skeptical of it's use in wall, floor and roof systems being a very (relatively speaking) new product to the market. I will wait for some years to see how real life testing of systems that have been in place for 20+ years are performing before recommending them to anyone, especially with the problems a foamed system will create when needing to renovate or chase future plumbing/wiring problems within these systems.