Inner sleeves versus none?

Hi. I recently bought about 70 albums from a personal collection. Interestingly, the guy used no inner sleeves - just had albums stuck inside the cover. I have been buying the nicer inner sleeves to replace the harsh paper ones in my own collection and was curious to see these records of his in pretty minty condition!! How can that be? Do you think he just used good equipment and that is the difference or is no inner sleeve a real option??? Please chime in before I invest more in inner sleeves. Oh - albums were from 1971 to mid 80s if that matters. Thanks!
Chapin99