Regarding "lost" ballots or "newly discovered" ballots-
dictionary.com/browse/provenance
provenance: place or source of origin
Ballots outside of the chain of custody have no provenance, they cannot be proven to be legitimate. That chain of custody has to be tight and itself, proven. Not transported in someone's car or random boxes "left" and discovered later. The chain of custody is broken.
That's just for one category of election fraud. You can, of course, have nefarious elements within an alleged chain of custody.