It sounds to me like the captains bars were used to denote the big engine available at the time. In '53 there were no 261's, so the 'big' engine would be the pressure 235, with the standard being the dipper 216. Then in '54 when the 216 was gone the captains bars went away on the 235 because it became standard and then when the 261 was introduced in '55 the captains bars came back and got used for it.
