GE6550 - variations in height

I have recently bought some GE6550 NOS tubes, and they sounded wonderful. but then there was a weird sound, just a second-long distortion coming from the speakers on the launch of the amp, so I decided to ask my tube amp designer to have a look. On examining the tubes, we noticed that one of the tubes looked suspicious, but as I had bought the tubes in a factory-matched set of 5 (one spare), we decided to replace the suspect tube with the fifth one, and then we noticed that the fifth tube is smaller. Is this normal? Can the GE6550 tubes actually differ in height??? The tube otherwise looks legit...