"Head" and "tail" were ambiguous meanings when I wrote the OP. That's why I precisely defined each, for clarity. Relative position becomes less important and, nomenclature becomes less precise when dealing with a T-shape headlamp, because there is no conventional head-end (reflector) or tail (usually for cell access, often including magnet). Hence my decision to offer definitions. I do agree that "tailcap" is generally the removable negative end. Except when it's not, a la FW3A.
I chose the define "tailcap" as the one that has the magnet in it only because a magnet is almost universally a feature of tailcaps AFAIK.
We can see good pics of the negative end in maukka's excellent review linked below.
In the 14th pic from the top, a tag is clearly visible inside the tube indicating the (+) end of the cell should be inserted first, toward the cap with the magnet.
In the 16th pic from the top we see the (+) lead entering the driver cavity through a hole at the left & soldered to a pad identified as (+) on the surface of the driver. The other end of that wire is soldered to the edge of board that is under the (+) tube cap that has the magnet. That's where it broke on mine.
18th pic is of the owners manual. At top left ti clearly reads "...untwist the tailcap or the head.." to achieve lockout. I suspect that's a carryover from another, conventional handheld light. At any rate, it's an error for the Panda 2M CRI.
https://budgetlightforum.com/t/-/55413
Now lets look at an illustration of the Panda 2M (not the CRI version) on the YLP site itself. Same light but with a pair of XP-G3's this time. The (-) end cap clearly indicates it's the one to be removed. That curved-arrow graphic doesn't appear on the 2M CRI. Instead, there is simply text that reads "HI CRI. Which cap is to be removed then becomes ambiguous to an observer.
https://ylplight.com/en/katalog/1/nalobnye-fonari/panda-2m/
It had been many months since I'd first installed a cell in my 2M CRI. I didn't remember which cap to remove, so I simply grasped a cap in each hand & twisted. I must have tightened the (-) cap fairly tight the first time months before and, the light's body had heated & cooled a few times during use, perhaps effectively tightening the (-) cap a little further. At any rate, there was insufficient glue on the threads of the (+) cap to keep it from turning.
slmjim