The Isles of Scilly get called by varying titles. In the media, on television programmes and in newspapers & magazines, we hear the islands often being referred to as the Scilly Isles or the Scillies.
The official title is of course the Isles of Scilly, but people can be forgiven for mis-titling due to the media.
Old maps dating back from a few centuries ago often title the islands as the Scilly Isles. I love looking at old maps of the islands. You see varying shapes & sizes of the islands and their coastlines as the more primitive forms of cartography were used to map the area. The more rugged maps & charts are well worth a look if you get the chance.