I'm not an expert on legal states and how they do their labelling but from what I understand the brownie itself will have ~100mg total in it, yet the dose is not an entire brownie. Rather, a single dose might be a quarter of the brownie, which would bring each dose down to ~25mg out of the ~100mg whole.
I'm pretty sure you're reading your labels right, though, because if you eat that whole brownie you for sure will be ingesting ~100mg. In my experience, it's easier to keep track of this kind of stuff when the doses are already broken down for you... like with chocolate bars or gummy bear-type candies.
In CA, laws require no more than 10mg thc per dose/edible. Not exactly sure what defines a "dose", but i'm pretty sure it needs to be partitioned already. Like gummy bears or tablets. Not sure about chocolate bars that have squares that equal 10mg, but brownies above 10mg are prohibited now.
There is still a ton of product available that is out of compliance though. A survey taken not that long ago said that only 1/7 shops in CA were compliant. Still a lot of places operating in pseudo legal/grey markets claiming prop215/sb420 medical. Ironically enough, these are the places with some of the dirtiest weed. There are a lot of weed festivals, meet-ups, private events, and flea market type gatherings where "vendors" line up and sell with little to no regulation or oversight.
Should be interesting to watch as things continue to unfold. So much drama happening in the weed scene. People getting desperate and robbing friends/associates. Employees robbing employers, employers scamming employees. Permitted growers, manufactures, distributers, retailers snitching on black market operators and getting rewarded by the BCC and other governing bodies.
The new testing regulations implemented on July 1st began to expose a lot of dirty companies that claimed things like "all organic" yet popped for myclobutanil or similar pesticides. The crazier thing is that there are still a lot of chemicals being used that are undectable by current testing standards. Certain PGRs, some lesser known pesticides or herbicides, and so on. It's finally becoming well known that current cannabis lab standards are basically non-existent, and it wouldn't be hard for a grower, distributor, retailer, or lab to tweak the results.
Just glad that I still have friends that grow awesome weed.