Map Drop Question

I have completed T15 Reef Map on my Atlas, no other T15 or any T16 maps. Also, I have not elder-orbed any map. So when I play a Reef Map I will be able to drop T16 Lair of the Hydra Map since it is connected to Reef but no other other T16 map. Correct?
Main question is: When I buy a T16 Elder Underground Sea Map from another player, can I drop Lair of the Hydra in it or will the T16 drops be downgraded to T15 and I drop Reefs?
Thank you for your help!

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VValnuss wrote:

I have completed T15 Reef Map on my Atlas, no other T15 or any T16 maps. Also, I have not elder-orbed any map. So when I play a Reef Map I will be able to drop T16 Lair of the Hydra Map since it is connected to Reef but no other other T16 map. Correct?

Correct

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VValnuss wrote:

Main question is: When I buy a T16 Elder Underground Sea Map from another player, can I drop Lair of the Hydra in it or will the T16 drops be downgraded to T15 and I drop Reefs?
Thank you for your help!

If you unlocked Hydra before you start running T16 UGS maps, Hydra maps can drop.
Otherwise T16 drops will be downgraded to T15.

Same is true for the temple. If you run at least 3 T15 Incursions, the temples lvl will be T15 too or T16, if you run 3 T16 Incursions.
This way mobs in the temple can drop toptier maps as well and so does the carto room.