Experiments show that cosmic ray muons reach Earth surface in greater numbers than they should, unless relativistic time dilation is taken into consideration. It also seems to confirm the SR formula mathematically. However, looking at a lot of different experiment records, I have some doubts about the validity of the experiments. I would like to get an opinion from those in this forum who are knowledgeable in this area. My questions are: 1) Consensus looks as if the cosmic muons travel at about 98% of the speed of light, and therefore have a γ of about 5, and some experiments confirm this. This seems to confirm the SR time dilation formula with a very high precision. Now, there seem to be some different experiments showing different γ's ranging from about 5 to 189 (based on what I can find on the internet). Why this variation of γ? Is it because different experiments focus on different energy levels of muons? Which are the reliable/officially accepted experiments? 2) There also seems to be an assumption that the cosmic ray protons produce muons at an altitude of about 15 km (~ 9 miles) from the Earth surface. Is there any validation of this assumption? Where did this assumption come from? Should the protons not be creating muons at various altitudes (perhaps with some sort of Poisson distribution between altitude and muon numbers produced?) Is this assumption a necessary one for the purpose of validating the SR formula? One overall question - how valid are the cosmic muon experiments as a proof of relativity theory (i.e. is it among the top proofs, or low down in the order)? I am not questioning the fact whether muon lifetime does get extended (which I accept), only how valid the "exact mathematical application" of SR formula is given what seems to be somewhat fuzzy assumptions? Any insights will be greatly helpful.