Quote from: LoyceV on August 30, 2018, 08:53:34 AM

Blocks get orphaned all the time, and as far as I know the orphaned transactions aren't abandoned, they're just added to other blocks again.

This applies to 'normal' transactions.

But maliciously sent transactions which aim to create a double spend do leave transactions inside orphaned blocks which aren't later added to the main chain.

So while the majority of transactions has been added to the mainchain through other blocks, a few have not been added (which are still valid itself in terms signature check).