I'm curious what's double enchanting staff are you talking about ?
I remember this one from an old PC thread : RE: OS BDS Dual chant staff? but imo it was an obvious photoshop (notice the weird spacing of the enchant mod)
This one, yes, the BDS. For some reason I remembered 19—20%, now I see it says 20—15%, I never read the thread and I just took a quick look at the picture in its moment, my fault.
I'm reading now the thread and yes, it seems fake, the explanations given by Surge are logic and makes sense.
It was 20% of enchant length +20% of enchant length.
It was not 24% of enchant length.
That is why it was broken. And retroactively nerfed.
What I wrote in the wiki is that the sum of both 20% increased the time to +40% due stacking (as a bug or whatever, and also being this the reason of the removal), conducted by the lines: (...) that could be modded to double 20% enchant. (...) and "At the time there wasn't a way for permanent spell immunity solo except until that axe was discovered."
I mean, to put in context why I wrote that:
1. Sword Pommels (of Enchanting) as far as I know existed since the beginning of the game, so the Denravi Sword (which also existed since the beginning) could be modded with a 20% enchanting.
2. Spun said that "at the time there wasn't a way for permanent spell immunity" (until the discovering of this axe), so saying this I assumed that in this time a normal 20% enchanting was not enough to having a spell permanently active (Denravi Sword assumption discarded then), because many skills have changed over time and I never played the very beginnings of the game, so it could be that the duration of some skills at that time was much much less than it is today.
3. So regarding what I understood before, I assumed that this axe was a mistake by ArenaNet's part and the double 20% enchanting had an effect stacking, creating an unique 40% (and that this was the reason of the removal when they discovered it).
4. Hobo said "NO" to my point 3, so if this effect was not stacking like he says, then it means that it doesn't matter the double, triple or infinite enchanting, the effect of the axe was just a normal 20% like the Denravi Sword with a sword pommel.
So, it stacked or not???? xD