I went ahead and broke the box seal on one of my new GP spares. The "neck down" taper is more like 3/4 of the way to the tip - not half way.
Got mine here on FastLane.
Part No is 0 250 201 039 as stamped on the GP itself and also on the box.
I would not be surprised at all if Bosch had more than one marketing level of GP product - kinda like spark plugs. The "Duraterm" may be some slightly different product line from yours. It also says "Made in France".
I never trust the people behind the counter to give me the right part. I always match up the new part with the old. I've seen people get new spark plugs on gas engines that were too long - if they had put them in it might have cracked the piston. So, I matched up the new GP with the old, not that I expected any difference - and they were the same length. (I don't think GPs can crack the piston, I believe they are in the "pre-chamber".)
On our cars the GP numbering is from 1 to 6, starting at the front of the car and going to the back. That is also the cylinder numbering.
I don't know how well your car starts, but with only one bad glow plug on mine, the engine spewed out a lot of unburned diesel smoke and ran rough until it warmed up for about five minutes. Now I get just a puff of smoke and it runs smoothly after about 5 - 10 seconds.
Good luck on the task.