1) they add a common footprint to the domains you're using to create a pbn. if all of your PBN domains have a whois registration date within a few months, that's a red flag
2) studies have shown that domains without a whois lapse have higher success rates
i'm not really looking to debate the merits of whether or not it matters. i see that you sell domains that are all expired/re-registered so i understand you probably have a different point-of-view.
whether or not i'm wrong in looking for this, i'm still wondering how to ensure the domains i purchase through auction will have an uninterrupted whois history.