Gardiner lists only the common forms of Egyptian hieroglyphs, but he includes extensive subcategories, and also both vertical and horizontal forms for many hieroglyphs. He includes size-variation forms to aid with the reading of hieroglyphs in running blocks of text. (The Budge Reference has about 1000 hieroglyphs listed in 50 pages, but with no size varieties.)
Gardiner does not cross-index signs; once put on the list, other significant uses may be overlooked. One example of this is G16, nbtỉ, the ideogram for The Two Ladies, goddesses Wadjet as cobra and Nekhbet as the white vulture. These are the protecting and patron goddesses of the separate Egyptian kingdoms that joined into Ancient Egypt, who were both then displayed on the uraeus of Wadjet when the unification occurred and afterward considered jointly to be the protectors of Egypt and the pharaohs. This ideogram is listed only on the bird list as G16, and overlooked on the deity list and the reptile list.
Other subcategories included by Gardiner are abbreviations and personalized forms, and also a complete subset, used on papyrus, specifically for the Book of the Dead.
Budge, Sir E.A.Wallis, An Egyptian Hieroglyphic Dictionary, in Two Volumes, Sir E.A.Wallis Budge, (Dover Publications, Inc. New York), c 1920, Dover Edition, c 1978. (Large categorized listings of Hieroglyphs, Vol 1, pp. xcvii–cxlvii (97–147) (25 categories, 1000+ hieroglyphs), 50 pgs.)