The proper person to ask this question is the private attorney or public defender who represented him in California & was familiar with all the details of his past criminal record.
This is not intended to be legal advise or as legal representation. I am a California personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters.
As Mr. Crosner wrote, you're asking in the wrong place. You're also the wrong person.
This is a California specific question, which is why I'm not grabbing my partner to answer it.
On top of that, it will depend on the facts, and confidentiality will stop your brother's attorney from fully discussing with anyone else.
I believe your question is why your brother didn't get credit for the time he was out on probation. You don't get credit for time you didn't serve. Let's say I were sentenced to 40-180 months, and that time was suspended, meaning I don't actually do the time. I would be given probation up to five years (or so). If I violate probation halfway through, they still call in the original 40-180 months. You don't get credit for time on the outside.
It sounds like your brother has some credit for time served, and might have an argument to run some of his California time concurrent with this Arizona time, though. You're going to need to consult a lawyer in California who would make a motion to grant credit for time served in Arizona. It is ultimately up to the California Judge whether a sentence is run concurrent and credit for time served would apply here.