Legal Question in Business Law in California

I don't know who told you that. It is entirely wrong. A document is not filed until it is received by the court, opened and entered into the court's records.

What usually matters is when the document reaches the clerk's office. There are exceptions to this rule, but not for complaints in California small-claims cases. However, there are several reasons why a limitations period can be tolled -- in other words, the clock can stop ticking for a while under some circumstances. It's also possible that your limitations period was longer than you believe. The rules are complicated, and often depend on the specifics of each case.

A document is considered served on an opposing party when deposited in the mail (with an exception for service of the summons and complaint). It is not considered filed at that time. It is considered filed when received by the Court.