This was a case of my understanding being in error.
I received a signature “Kangor, Dancing King” from my silver rank bundle, which I already owned in the normal version. I did not receive the prompt to re-roll my normal version into another legendary from Festival of Legends.
The reroll offer applies when you find a “more special” card while already owning a “less special” card, and when that “more special” card cannot be disenchanted.
Signature Kangor, Dancing King can be disenchanted, though. So it does not meet the condition for offering a reroll of the normal version
I see, thank you for the answer. One more question, should it have been possible to receive “Kangor, Dancing King” as my signature? I was expecting it to be a signature of a legendary I did not already have since I do not own all the legendaries from Festival of Legends.
If you previously owned some of the legendaries but decided to disenchant them, that still counts as “owned” for purposes of duplicate protection.
Are there legendaries in that set that you have NEVER owned?
Yes. I just checked my collection progress for Festival and there are three legendary cards that I have not gotten in any form.
Do the three missing cards exist as Signatures? If not, and it rolled a Signature, it would have to give you a duplicate.
What are the three missing cards?
I always seem to forget that only a few select legendaries are given signature treatment, and I managed to collect all of them in their normal versions. Thank you all for clearing everything up.