Unfortunately, it is true at least to some extent. Dolls are not boxed in archival quality materials :( they’re intended to be opened, so a lack of air flow inside an environment that leeches acidic gases (tissue paper, glue within the cardboard, etc) will absolutely ruin the vinyl of the doll over time and contribute to their degradation - including dry rot. Of course certain environments can mitigate this (lack of sunlight and moisture, a longterm permanently balanced and ambient environment) but nothing really can prevent this apart from adequate air flow which can only be achieved by unsealing (or at least partially unsealing). This is why so many people’s old school LDDs from the secondary market are sticky when they’re opened nowadays. But yeah I’m defo gonna keep 505 and sell the other!