|"If they are deleted then they are not there, unless they are still in the bin."|
Actually, they are still there. Only the reference to them has been removed, and the space has been flagged as empty. Until the files are overwritten, they maintain a physical presence on the drive. The deleted files can be retrieved with recovery software (unless overwritten).
I guess you already know this, and were simplifying, because for all intents and purposes the space is available for use. Unless, as you pointed out, the recycle bin hasn't been emptied.
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