Does an A-number guaranteed USCIS acceptance?

The A number is assigned to any person seeking an immigration benefit or who was put into removal proceedings. The A number on the application has been assigned to the son you're trying to sponsor. Denials of I-130s are extremely rare.

The application has been accepted - meaning that someone glanced over it, found no errors and passed it forward to whoever will make the decision whether or not to approve or deny it.

You can track the case status online via USCIS.gov you can also sign up for alerts if anything changes (ex. the decision is issued or USCIS asks for more evidence).

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he 130 approval means they believe the family connection ..nothing else

its just the start of the process

Yes, it obviously has been accepted but sent to California for adjudication. Unless something is found wrong,

it should be approved.

Not at all, until such time as you get the "welcome to America" letter all the A number is, is a way to track your progress and status, plus you use every time you write to them.

Call them and clarify.