Campden Tablets / Sulfites - Some older recipes may omit this because
it wasn't readily available years ago. Others, like you indicate,
consider this part of the process and assume that you will add it at
the right time.
Sugar - Recipes differ because of different assumptions they make on
the sugar content of the fruit in question, and also due to the
desired outcome (sweet, semi-sweet, off-dry, and dry wines).
Yeast Energizer/Nutrient - Differences may be due to preferences of
the wine maker (recipe maker), recommended yeast, or simply what was
available when the recipe maker was working on the recipe.

Generally, it's best to understand the chemistry and biology of
winemaking, and have the tools in hand to test for acid, pH, and
gravity (sugar). I consider a recipe as a starting point.

Greg