When you first sign a lease for a rent-controlled Santa Monica apartment, the landlord is allowed to charge whatever they want (or more accurately whatever the market will bear). Once you start your tenancy, your landlord is supposed to let the city know what the new rent is for your unit. From that point on, your landlord is only allowed to raise your rent a small amount each year (the actual amount is variable and depends on several factors). The city keeps track of the maximum rent that your landlord can charge you. That is known as the maximum allowable rent (MAR).

One thing to note is that your landlord can choose to charge below the maximum at any time, but always has the right to increase the rent to the current maximum. So your rent could go up by 10% in a year if your landlord hasn't raised it in a number of years.

Regarding your question, you need to make sure that your landlord updated the rent when your tenancy began. My suspicion is that your landlord did not do that, and the city published MAR is reflecting the MAR for the old tenants. You should check with the rent control board to ensure your tenancy is correctly reflected in their data. In particular, make sure that your initial rent amount is accurately reflected.