Despite the oddities, looks to be a genuine (regal) piece. The missing chunk is likely an as-made planchet issue - these seem to be particularly common on that year's Zacatecas pieces (1836 is also coming mind, though not as often).
The other thing with Zacatecas pieces from the 1830s in general... the weights are all over the place. I've seen them range from down in the 25._ level to as high as yours.