Would HMS be understanding if I left off a few PI letters for (what I think are) valid reasons? Applying this year - one PI was for an award that I conducted research for in a foreign country, and the PI wasn't English speaking. Another one was for research that I barely interacted with the PI for and essentially led on my own - with my only correspondence with the PI being them signing off on things like IRB, and serving as the last author on a submitted manuscript. Can I let the school know of this in some way? I have a letter from the other PIs I've worked with closely.