Chart cell whose names begin with 1I are Navionics S63. These have the same data as any other Navionics charts.
Cells beginning with GB are official ENCs produced by United Kingdom (UKHO). I know that their coverage of
Virgin Islands is excellent, and generally they have pretty good reputation.
The important point to keep in mind is that official S63 charts will come from variety of sources - each country may make their own. Some are better than others.