If you weren’t claiming luggage, probably not an issue as you would just be connecting via sterile concourses. But as you exit baggage claim you are entering PR aren’t you?

We flew into STT the last week of February. There was a checkpoint outside after deplaning, and before baggage claim. USVI portal confo QR code,temperature check, and a paper copy of the negative WuFlu test had to be presented. If you were connecting in STT, you would have needed to comply with USVI protocol.

Obviously Five days is outside of 72 hours! And when checking into your flight to SJU the airline is likely only concerned with SJU PR arrival requirements. Are you on separate tickets, or one ticket with connecting segments? That may make a difference.