Bees should be fed honey from their hive only. If you have a large enough freezer and wanted to store say one or two supers from each colony and mark it so you would know it is theirs.
It is recommended not to feed bees honey from another colony.
Of course no one but you would know.
Their is nothing wrong with pure cane granulated sugar syrup. It is as natural as you can get in that category. doak