To me, it seems almost impossible to have a BOM with 100% Mil-spec parts these days. I have a hard time believing that even a deep-pocketed defense contractor can get TI, et. al. to make military grade versions of their normal stuff.
I thik many mfgrs parallel run production but test and bin their best parts for MilSpec then tun them thru tighter testing and assurances. Mil Spec covers all specifications of the part from tolerances, temp ratings, radiation hardened, QA inspection, storage and test process even the manufacturing conditions...yada yada yada.
I pulled up an old USA electronics parts 1987 MIL spec doc....for a gander...was stating that for Metallised Film capacitors must be +/-2% tolerance and this was measured at end of life. I have no idea how they determine EOL, Jeez that's tight.
So yes, the only way you can guarantee this is to be a certified Mil Spec parts supplier meaning your parts will not be cheap this is why these Acft cost so much. To think the buy price is just a portion, the ongoing life support costs are far higher.
This doesn't mean everything is perfect. I've seen repaired F18 flap from external supplier repaired to Mil Spec.....we boroscope inspected thru its weep holes..could see de-bonded rivets not clinching alloy doubles and carbonfibre. The crap that some suppliers tried to get away with defies belief. F18 flir LASER assy straight from factory.....qty 10, 2 were rattling inside...loose or extra screws...total fail.
So much for standards.