Yes, Jim.
These things are not linear indeed; let's confuse them a bit further
.
According to Dudley Gingell, the letter S transposed over a T and surmounted by a G belong to Jusepe de la Hera, both younger grandson and great grandson. Amazingly in Palomar's nomina it belongs to all viejo, mozo neto and visneto, the last two with the mention 'la misma' (the same).
In any case never to Pedro Hernandez whom, according to Gingell, used a P, a F, a crucifix and to other figures, one apparently the proof mark T for Toledo.
The same Gingell assumes that Sebastian Hernandez the younger, besides his father crown over a 3, also used the wild man. The confusion increases when Gingell shows a panoply of marks for Sebastian the older, namely the 3 under two types of crown, a S under a cross and a F under a cross, with another cross on the estucheon.
In trying to figure out the meaning of the symbol 3, one finds a theory in that the symbols used by Toledo swordsmiths for their marks were not necessarily the initials of their (usualy) first names but some kind of symbols of contrast indicating the quality of the blade (Florit and Sanchez Canton in Catalogo de las armas del Instituto de Valencia de Don Juan - page 63). In fact, the symbol 3 is also used by Fernandez Ignacio, the younger, for one.