For whatever reasons Osmocote® Exact® and so forth are not available in North America, Osmocote Plus seems most closely to match Osmocote® Exact® Standard High K, which for North America would still be low-side K.
I find most of this to be true for Osmocote® Plus® and Osmocote® for that matter.
The variation I have observed is the “Temperature influences on the longevity” chart on page 16, I find the chart red “M” 3-4 to be exactly what I am seeing with Osmocote® Plus® in the water, at least for the 25-30°C range.
What I am observing from Osmocote® Plus® in the substrate of a dozen tanks, used at the light container gardening rate, is closer to blue “M” 8-9 for 25-30°C.
As to Osmocote® Plus® losing its humph after a few months, I have the Osmocote® Plus® I purchased a little over 3-months ago for this investigation sitting here on my desk. I have opened it several times and hand tightened the cap each time, the temperature in here has pretty much been between 23.9°C and 28°C. They look all right, a bit of dust settled in the bottom. I will test some. If they leaked, I assume I will find a heavy concentration in the bottom.