You have met your obligation by appearing as promised and the clerk has provided you with proof. The case may have been lost in the shuffle or filed in the wrong court. Sometimes cases disappear and sometimes they show up. The statute of limitations for this type of case in California is one year, so it can be prosecuted within one year of the date of the offense. Depending on the circumstances, you may have a defense based upon speedy trial rights for delay that does not arise to one year. The ticket has to filed before it can be dismissed.
My area is mainly criminal law, not infractions, but it would be prudent to continue to check with the court clerk's office once a month to ensure that the infraction has not been filed. If the infraction is filed and you do not appear you probably will be assessed fines and have your license suspended in absentia (without you being present). You do not need to go to the clerk's office in person to see if the infraction was filed, you can call instead. Also, if the matter is a LA County case you can check the website and search by the infraction number and your driver's license number: http://www.lasuperiorcourt.org/traffic/ You probably should continue to check monthly to see if the infraction has been filed for at least 12 months. Good luck.
Don't call every month. It will only remind them that your case exists. Eventually they will find it and get you in court. Lay low and sometimes these things slip through the cracks.
By the way, infractions are part of criminal law as well as misdemeanors and felonies.
I am not certain why you would go to juvenile court rather than a general "Infraction docket". Only criminal traffic is held in juvenile court. Have you asked the traffic infraction clerk? Often times infractions are not put in the same place as criminal charges. Thus, they cannot be seen by another computer.
Yes, cases have been dismissed for lack of prosecution, even in civil infraction court.
I do not practice in ca but these are general rules which may be applicable.