Take part of this with a grain of salt. Captain John Prater, immediate past-president of ALPA, was the secretary-treasurer of the CAL MEC during the 1983-85 strike. Needless to say, he didn't cross the picket line. Nevertheless, his employee number ends with a letter. So do the employee numbers of certain Frontier pilots, who came onto the CAL seniority list well after the strike had been settled. Old Cal plots who crossed the picket line don't have letters in their employee numbers. I've been told, but can't say for sure, that even some old strikers who got fired during the festivities, and then got their jobs back during the grievance process, were then assigned employee numbers with a letter on the end.