Additional context of the lifetime transfer to partner

Although I am sure this isn’t part of the syllabus, or at least I don’t think it is, when discussing the lifetime transfer of the nil rate band to spouse/civil partner upon death – I was wondering if this is lost if the widow/widower remarries?

Further to this, if the newly married partner then also dies, would the previous widow/widower retain the new partners nil rate band if he/she hadn’t made use of it? My thinking here is does the lifetime transfer accrue to the widower/widow indefinitely depending on how many partners of theirs die.

For example, if a woman married 4 times in her life but all partners unfortunately died, would the nil rate band (assuming unused) be transferred to the woman from all her partners for her to offset on her death.

Very morbid question I know but is useful for how my brain works in remembering this stuff lol.