Again, unless you can trust the data in the IRR to build a complete list of valid AS Paths from the ORIGIN, you can’t safely reject a fake route that has the correct prepend.
Or you can have each hob validate. For example if HE.net did RPKI validation, it would be effective due to their large number of peerings. If my network has HE.net as one of my uplinks, someone might fake the route via one of my other uplinks, but we would not pick that route due to longer AS path.
Regards
Baldur