Carbine were mixmasters when issused as there was what 20 subcontactors suppling parts to the 6 companies building the M1 ,parts were dumped in to bins on the line and grabed as needed and once the M1's went to depot for rebuild , all the parts were pulled dumped together ,cleaned ,inspected and replaced as needed
Actually, parts on Carbines at the factory received markings that made them correct for that Carbine manufacturer, regardless of who made the part. So to call a factory-issued Carbine a mixmaster isn't quite accurate, otherwise you wouldn't have had untold numbers of collectors over the decades trying to correct their arsenal-mixed Carbines