According to our current understanding of particle physics, all protons are considered to be identical. In the standard model of particle physics, protons are elementary particles with no substructure. They are composed of three quarks (two up quarks and one down quark) bound together by the strong nuclear force.
The assumption of identical protons is based on experimental evidence and extensive observations. Many experiments have been conducted to measure the properties of protons, such as their mass, charge, and magnetic moment. These experiments have consistently shown that protons exhibit the same properties regardless of their origin or the conditions under which they are studied.
However, it is important to acknowledge that our current experimental techniques and precision have limits. There is always a possibility that there could be extremely small differences between protons that are beyond the capabilities of our current instruments to detect. This concept is often referred to as "beyond the standard model physics."
Scientists continue to conduct experiments and pursue research to test the limits of our current understanding. If any deviations or differences were discovered in the future, it would likely require advancements in experimental techniques or the development of new theories to explain them. So far, the evidence supports the assumption of identical protons, but scientific inquiry remains open to further investigation and discovery.