Their English
website page for XT-3 does say, "with improved storage capacities compared to earlier ascorbic-acid developer recipes." And, "Better keeping properties" compared to "similar working recipes like Xtol, Excel or LegacyPro Eco."
However, when we move from the general product description to specific recommendations, Adox says,
"Once mixed XT-3 should be filled in dark glass bottles filled to the top or topped up with protective gas (alternatively throw in clean glass marbles to taise the level of liquid). Prepared like this the stock solution should keep at least 6 weeks and
up to 6 months depending on storage conditions and depletion of the solution."
The most recent data sheet I can find for Kodak XTOL is from Alaris,
Publication J-109 dated Feb 2018. And that data sheet gives the shelf life of stock XTOL "in full, tightly closed containers" as "
6 months."
So really, both manufacturers are claiming the same shelf life for the mixed stock solution -- six months -- right?
Actually, the exact wording used suggests Adox XT-3 is good "up to 6 months" (a maximum of 6 months), and Kodak just says "6 months" suggesting a minimum of 6 months?