The definition of level adjustment in the glossary describes how the presence of such an entry in a statblock (when it's a number instead of -) means the creature is available as an option to players:
Quote Originally Posted by Level adjustment
Certain monsters can used as the basis for interesting, viable player characters. These creatures have a level adjustment entry, which is a number that is added to the creature's total Hit Dice to arrive at its effective character level. A creature with multiple special abilities is more powerful as a player character than its Hit Dice alone would indicate. For example, a drow elf has spell resistance, bonuses to its ability scores, and spell-like abilities. Its level adjustment of +2 indicates that a 1st-level drow wizard is the equivalent of a 3rd-level character. [...]
As spellstitched (CA) lacks such an entry, it's by default equivalent to a LA - template. So yeah, spellstitched necropolitan PCs shouldn't be a thing.