While it is hard to prove this for Demodras specifically as it is also available as a task, we can infer from other bosses that have multiple spawn points (or in fact, multiple possible unannounced raids) that they can spawn in their different spots within the same 24h window.For instance, this has recently happened in Secura for White Pale on 21-09-2022. I witnessed both kills, one in Liberty Bay and another in Edron, and this data point is visible on GuildStats kill stats tracker as well [link]. If you browse kill stats for other bosses you will find more examples :)
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