More details about this issue.
If you install a CIA you haven't ever purchased, it will leave a fake ticket on your ticket.db eternally.
Only System Transfer & Restore ticket.db/NAND backup (if it doesn't contain the fake ticket) can remove it.
This fake ticket has Console ID 00000000, which is recognized as a "pre-installed" content.
Nintendo e-shop will not force your 3DS deleting "pre-installed" content even it's non-legit.
If you have purchased at least one content of a title (e.g. 1 Fire Emblem Awakening DLC of 26 total), it will leave a valid ticket on your ticket.db eternally.
Only System Transfer, Restore ticket.db/NAND backup (if it doesn't contain the valid ticket) & Delete NNID (linked to your valid ticket) can remove it.
This valid ticket has Console ID = Your own Console ID, which is recognized as a "purchased" content.
Once you have the valid ticket, Nintendo e-shop will force your 3DS deleting everything within this title unmatched to your valid ticket.
Fake ticket & Valid ticket can't be replaced each other.