No, it is not too late for letters if you fall into one of two situations:
1.) If you have yet to submit your applications for residency, then you are still free to ask for letters of recommendation. Obviously, this situation is not ideal, but it is plausible.
2.) If you asked for a letter of recommendation from a faculty member, had it finalized on ERAS for submission, but have yet to have that letter sent to your medical school, then you are free to remind/ask for your letters of recommendation.
The second situation is one that I find myself in currently. While three of my LoR's are currently uploaded, my fourth has not been. Apparently the letter writer forgot to add "This person waived their rights to view this" in the body of the letter and my school felt it was unacceptable for submission. I have since sent him multiple emails, but with no success. Fortunately for me, I am going back to that hospital in two weeks, so hopefully I can ask him face-to-face.
TL;DR: It isn't too late, depending on your circumstance.