They carry forward enormously, the USMLE is basically your basic sciences applied to clinical scenarios. The big payers are physiology, pathology, pharmacology, microbiology, and biochemistry. If your foundations in those are shaky, Step 1 becomes a nightmare of relearning under time pressure. If they're solid, you're refining and applying rather than learning from zero. For Caribbean students aiming at US residency, strong board scores are how you overcome the IMG disadvantage, and those scores trace straight back to how well you built these foundations.