In this comment, I would like to describe the difference I perceive compared to the reissued fragrance from 2014. All detailed information about that fragrance and the history of the Lang scents can be found in my comment on it.
I will start with two quotes from the perfumer Maurice Roucel (also responsible for the reissue and creator of, among others, Lalique pour homme lion, Musc Ravageur, Dans Tes Bras, Helmut Lang EdP, New Haarlem, Rochas Man, Nautica Voyage, etc.), who responded to the question "What has been done to reinvigorate it?" with the following answer: "Concerning the formula of the perfume… nothing. It is simply a rebirth." (Source: https://i-d.vice.com/en_uk/article/pabgvg/the-smell-of-nostalgia-with-helmut-lang). However, his remark in another interview from 2015 suggests that there may have been changes that he believes are not perceptible. There he admits to the question "Has the formula changed?" - "No, not in any discernible way..." (https://www.cafleurebon.com/cafleurebon-behind-the-bottle-interview-with-maurice-roucel-helmut-lang-eau-de-cologne-helmut-lang-eau-de-parfum-draw/).
So, it is actually the same fragrance. Actually, because I already perceive a small difference. The pyramid (or non-pyramid, which I cannot understand here at parfumo for the successor, as it already has a progression and is better represented, in my opinion, at fragrantica and basenotes) also has partly different ingredients.
Fragrance progression:
In my opinion, the most noticeable difference is the greater freshness of the original, where the lavender note seems more pronounced to me. This freshness pulls through and holds throughout the fragrance, while in the successor it is not as pronounced (no lavender in the "pyramid") and is quickly replaced by a subtle, yet dominant vanilla note. In the original, the heliotrope note is at the center, sweet, clean, and slightly vanillic, mainly supported by the lily of the valley. This fresh sweetness makes the fragrance softer and (still) more innocent. Compared to the 2014 fragrance, this slightly erotic note hardly comes through, and the fragrance resembles clean baby powder, but still carries the intimate skin scent within it. This effect is primarily caused by the Givaudan musk molecule 'Velvione', which forms the heart of the base in this and the EdP (https://hbw.pharmaintelligence.informa.com/RS009013/Helmut-Lang-Singles-Out-Velviona-For-Latest-Fragrance-Offering). Its odor is described as musky, sweet, powdery, animalic, and strong. Maurice Roucel also sees it this way in an interview in 2015: "Helmut Lang Eau de Cologne is one of the muskiest perfumes on the market and is my musk masterpiece." (https://www.cafleurebon.com/cafleurebon-behind-the-bottle-interview-with-maurice-roucel-helmut-lang-eau-de-cologne-helmut-lang-eau-de-parfum-draw/). 'Velvione' belongs to the category of macrocyclic musks and exhibits properties of nitro musk molecules, the first synthetically produced musk molecules, and was even launched by Helmut Lang as an independent fragrance "Velviona" in 2001 (in a limited edition of 500 pieces). Therefore, it is considered the first of the so-called "molecule fragrances," which became popular mainly through Geza Schön. Compared to the 2014 fragrance, I also perceive the woody note to be less pronounced, which makes it seem a bit less "masculine."
Longevity and sillage:
The longevity is quite decent for a cologne, just like the successor. It is very noticeable on my skin for 2-3 hours, although fragrances usually last below average on my skin. After that, it remains softly and pleasantly perceptible for another 5-7 hours. The projection only slightly exceeds skin level in the first hour.
Conclusion:
The original is the slightly fresher version and appears even cleaner and softer than its successor from 2014. Thus, the original intention of Helmut Lang, which he described according to Maurice Roucel as the design of the fragrance: "He wanted the jus to smell of his boyfriend’s secretions on clean sheets" (Source: http://www.cafleurebon.com/perfume-news-helmut-lang-relaunches-helmut-lang-eau-de-parfum-cologne-and-cuiron/), is better fulfilled, especially for the second part of this expectation. In my opinion, the first part is better captured by the successor fragrance.
I also have the impression that the original is somewhat less synthetic. I am talking here about hardly perceptible artificiality, which shows in nuances in the woody drydown of the 2014 fragrance.
In both cases, it is an absolute unisex fragrance, as the successor is also marketed. The original was still labeled as a men's fragrance.
As my comment on the reissue page shows, I am a big fan of this fragrance and now of both versions.
P.S.:
In addition to many other great reviews here about this fragrance and also the comparison of the two on the successor's page (Terra, DaveGahan101, Grabsplatter, Apicius), there is a very detailed one in the YouTube comment by Siebter (see below).
Additional info:
(added on 07.07.2018)
Thanks to the hint from dear Parfumo member ivko, I learned that the fragrance was already available for purchase before the official release in 2000! After that, it was already distributed, along with the Eau de Parfum, from 1997/98 in a men's boutique called "Holy's" in Stuttgart. Holy's was run by the Holy brothers, grandchildren of Hugo Boss, who were at the top of the Boss company for many years, later launched Strellson and Windsor, and after leaving the Boss company in 1995, founded Holy-AG. This AG still operates the Outletcity Metzingen today. According to ivko, the bottles at that time had silver caps, which can also be seen in the video by Siebter. At some point, they must have switched to black caps. Unfortunately, I have not yet been able to determine when this change occurred and whether something about the character of the fragrance changed in the process, as it is currently not possible to "decode" the batch codes of the Lang fragrances online. An email inquiry to the Helmut Lang Customer Service regarding this also went unanswered. The staff had no way to find that out.
Anyone with further information about the fragrance is welcome to contact me. I would be very happy and grateful for any hints :)
Top Notes 
Lavender
Rosemary
Heart Notes 
Heliotrope
Lily of the valley
Jasmine
Rose
Base Notes 
Musk
Cedar
Sandalwood
Patchouli
SchatzSucher
Toppine
Pluto
Stulle
Jacko
Parma
Yatagan
FFL
Medianus76
Mustang69
