What do you think should those missing stamps be added as new items or should they be mentioned as variants for an existing item? There are such differences as purchasing date, different watermarks and smaller differences in items, for example.
Deciding whether a stamp is a variety of its own (deserving a number and, more importantly, a separate entry here on Colnect) or just a curiosity is not always easy, especially if one uses a local, specialized catalogue as reference.
Errors, slight colour shades, tiny differences in the design are probably best left out, and only mentioned in the description field as wisely indicated by saintluc. This is particularly true when the value of this variety is disproportionally higher than the normal stamp (I might think it has been purposely done for speculation purposes).
On the other hand, a different watermark, perforation, paper, ... used for a large-scale reissue of the same stamp is definitely a variety that needs respect, and hence a place for itself. Usually, international catalogues will include them in their pages, or at least mention them as a little note.
I believe the main purpose of Colnect, and what the majority of its members expects to find here, is an easy and quick way to identify, classify and mark their own stamps, with or without a printed catalogue in their hands. If they do not have any catalogue, they will probably need just the essential information needed to tell a stamp from another similar item. If they do have a catalogue, they already have the right source of information they might need.
I am of the opinion that a specialized catalogue is NOT what most people want to see here. Information should be kept essential, or differential, in the sense that only differences should be pointed out where necessary. For example, what is the point of showing perforation, watermark, printing method if a stamp was only ever issued in one perforation gauge, watermark or printed in one method? The extra information is unnecessary for the purpose of identifying and classifying a stamp in one's collection. I often see description fields BLOATED with all possible details on the person being depicted in the design: I guess each of us can easily find the very same kind of information on Wikipedia, can't he?
The risk of putting too much detail, pushing on a high degree of specialization is clearly visible in Italy's 1950 year, as an example. Unless you collect all varieties of watermark direction, you will probably feel stoned after looking at that. The other day somebody argued that Austria's #1 stamp looks ridiculous here on Colnect, as there are dozens of different shades, and hundreds of different cancellations each having a different value. I suspect Colnect is not the right place for him.
