Sam never struck me as a character who would have even owned a suit - at least I don't *think* we ever saw him in one.
"OH, NO - we got rid of all of Sam's clothes - and it's too late to get anything from Ohrbachs now!""Don't worry, we'll just throw this trenchcoat over David's own clothes. After all, it's not like anyone is ever going to see this episode again..."
It simply wasn't done back then