Hello Curious and thanks for your question.
Until the seller actually accepts and affixes his/her signature to the bottom of a purchase contract, and unless the seller tells the agent "I do not want to see any other offers", the agent may present other offers. Typically, if the new offer is lower than the offer already being reviewed, it makes little, if any, sense to tender that second offer to the seller since a higher offer is already being proferred.
However, if the seller has already accepted an offer and is in contract, then we do not normally tender other offers except to tell the buyer that they can be a "backup offer" in the event that the first offer falls through. In most cases, this is true for short sales, so a backup offer is always appreciated. Otherwise, once a home is in contract, no further offers are accepted or reviewed.
And, Curious, it was never a "law" in California that offers had to be presented. In fact, I know many Realtors who will not even present a "low ball" offer to the seller, and there is no imperative that an agent "must" present any unqualified offers to the seller. It's our job to weed out or to direct buyers to the requirements necessary to make a qualified offer that can be submitted to the seller.
Hope this helps!
Grace Morioka, SRES, e-Pro
Area Pro Realty