Why is used ' sales records' instead of 'sale records'( 'cause the first noun of a compound noun is always in the singular form)?
Be careful with any rule you've learned that contains "always" or "never."
There are few rules that these words can really be aplied to.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.