The F17T8s in my basement have been up maybe a year or so and they are BLACK on the ends. Those cheesy instant start ballasts are really pushing those lamps. They're as black as the one above.
I had a F17T8 wraparound with a cheap IS ballast that made lamps blacken after a few months, eventually I just replaced it with a Cooper circline fixture.
I had a GE 40w mainlighter was black on the end like that when I moved into my house, and I had noticed the lamp had not been inserted correctly at that end. I fixed it and it lasted (at about 20 hours a month) for about 10 years. After it quit on the rapid start ballast, it took HOURS to fail on an electronic IS ballast.
Yep, these older GEs seem to be good lamps...you also mentioned this Mainlighter on a pic of mine and I have to agree...they will go practically forever with black ends sometimes!