The sign D396 D396 is a nice example of the problems we might have with sign lists.
The sign is not in the original "Manuel de Codage", nor in the original (black lead) IFAO fonts. In the Hieroglyphica (and in JSesh current fonts), the sign is made of the eye sign on the "qd" sign (Aa28). Now, there is a very complete article on the subject by H. G. Fischer, "An old kingdom monogram", ZÄS 93 (1966) p. 57 sq.
In this article, for a number of Old Kingdom instances, Fischer demonstrates that the sign below is M40 M40(ỉs) and not Aa28 Aa28. Yet : the signs for ỉs and ḳd are sometimes rather similar, and ... a late version of the ỉs sign is in fact used in place of ḳd in and after the Eighth Dynasty (ibid.)
Thus, the drawing which was chosen is not the most typical glyph for this character, although it's attested in some examples (for instance, Cairo JE 49691). In fact, it's slightly misleading, as originally, scholars did hesitate between the readings ỉr-ḳd and ỉr-ỉs because of this very shape.
Now, this brings us to the problem of erroneous interpretations of signs, which may give birth to "phantom" signs. A typical example for this is V491 V49 Our hieroglyphs are already interpretations of the original signs, and errors are probably unavoidable.
Now, what should be done ? Should we change the picture of D396, or create a new sign ? Things would be simpler if the motivations for adding the sign in the fonts were known. In this particular case, the current picture is known from the monuments, so the reasonable thing to do is to add a new sign.
Even if the original glyph did not exist (as in the case of V49), it would still be at least an egyptological object (if not an ancient egyptian one). Saying that V49 is a reading error supposes the existence of V49, in a way.
So, I suppose I will create US1D396VARA... with the "js" sign below.
An important remark on this: this kind of mistakes - if it's a mistake - is more or less doomed to happen in hieroglyphic lists. In fact, as long as egyptology is a living science, readings will be improved, and in some cases, it might impact the interpretation of signs. Now, the real problem is that it's really difficult to make choices if the sign lists are not documented.
A. H. Gardiner, "The Transcription of New Kingdom Hieratic", JEA 15 (1929), p. 48-55. ↩