While the number of mitzvos is generally accepted, what’s on the list can vary depending on the authority consulted. How is that? Well, first of all, not everything is clear whether or not it’s a command. Let’s look at two examples:
Exodus 14:13 tells us, “Moses told the people, ‘Do not be afraid. Stand strong and you will see the salvation that G-d will work for you today. You have seen Egypt today, but you shall never see them again.’” This seems like it’s simply part of the narrative, a prophecy perhaps, but Nachmanides in his commentary cites the Mechilta that it is actually a prohibition to return to live in Egypt. (In his list of mitzvos, Rambam includes the version of this prohibition that appears in parshas Shoftim, Deut. 17:16.)
When given the instructions for making the bigdei kehuna (priestly uniforms), the Torah tells us that “the robe shall have a reinforced neck hole … so that it won’t be torn.” Or, perhaps it says, “the robe shall have a reinforced neck hole … do not tear it” (Exodus 28:32). It is generally accepted that tearing the neck of the robe violates a Torah prohibition.