Hello Mark. The reason you are seeing conflicting instructions is that there are two distinct culinary traditions for savory tuna pies, and each treats the eggs differently depending on the crust and desired structure.
For the best texture in a standard quick weeknight pie, whisking the eggs directly into the filling (or making a light custard with a little milk or cream) is definitely the recommended approach. Canned tuna is lean and flakes easily, while cooked or grated carrots release moisture. When you beat raw eggs into the mixture, the proteins coagulate as the pie bakes, creating a cohesive binder. This traps the moisture, prevents the tuna from becoming dry and chalky, and ensures the pie holds its shape nicely when sliced.
Hard-boiled, diced eggs are traditionally used in enclosed pastry pies, such as a classic Spanish empanada or Latin American torta, where the filling relies on a thick vegetable sofrito or sauce rather than a custard base. In those recipes, chopped hard-boiled eggs are added purely for texture and richness, but they do not bind the ingredients together.
If you are making an open-top tart, a quiche-style dish, or want a clean, sliceable filling that stays moist, whisk 2 to 3 raw eggs, season well, and fold them into your drained tuna and softened carrots before baking. It will give you a tender, perfectly set texture.