(a) A claim may be amended at any time before the expiration of the period designated in Section 911.2 or before final action thereon is taken by the board, whichever is later, if the claim as amended relates to the same transaction or occurrence which gave rise to the original claim. The amendment shall be considered a part of the original claim for all purposes.
(b) A failure or refusal to amend a claim, whether or not notice of insufficiency is given under Section 910.8, shall not constitute a defense to any action brought upon the cause of action for which the claim was presented if the court finds that the claim as presented complied substantially with Sections 910 and 910.2 or a form provided under Section 910.4.