@Riot How does Adaptive Helmet work? (posting here, don't have PBE account [still])

Some time ago you've been talking in regards of TLD that you are working on tech that would recognize multiple instances of damage from the same cast of ability, disallowing DoT from single cast to count as multiple stacks towards TLD, which is why this came up to me.

If I get damaged by ability A and its first instance of damage, applying the passive, will subsequent instances of damage from ability A from that very cast still get decreased? So If Rumble firespits on me, will I take full damage only from the first tick and then take 15% less from any tick of that cast and any further cast as long as the passive lasts? Or does it only work on low-CD abilities like Cassio's teeththrower, reducing damage of all Es after the first one as they are different casts of the same spell, aimed for this item to counter non-DoT DPS magic damage?

Also, does this effect stack? As in, If champion throws entire combo at me (or even multiple champs) will I get this Passive in relation to each of their abilities or only for the first that dealt damage (from the first champ/per champ)?

Going into conditional extreme of One for All: If one Ziggs damages me via ball, thus making me take lower damage of subsequent bombs, will other Ziggs have their first cast of bomb lowered on me as it's the same ability (though different source), or does the game recognize source?

Thank you If any of you will actually stop here to answer. :3