What it must tell you. ERISA section 102(b) lists required content, and the list is more specific than most people expect. Among other items the SPD must state the name and type of administration of the plan; the name and address of the administrator, and of the agent for service of legal process if that is someone else; any trustees; the plan's "requirements respecting eligibility for participation and benefits"; a description of the provisions providing for nonforfeitable pension benefits, meaning vesting; "circumstances which may result in disqualification, ineligibility, or denial or loss of benefits"; the source of the plan's financing; the plan year; "the procedures to be followed in presenting claims for benefits"; and "the remedies available under the plan for the redress of claims which are denied in whole or in part." If you want the vesting schedule, the eligibility rule, or the appeal procedure, the SPD is where Congress required them to be.
The delivery schedule, all of it in section 104(b)(1). A new participant gets the SPD within 90 days of becoming one, or within 120 days after the plan first becomes subject to the statute, whichever is later. Every fifth year the administrator must furnish an updated SPD "which integrates all plan amendments made within such five-year period," with an exception if no amendments were made. Regardless of amendments, an SPD must go out every tenth year. In between, changes are reported through a summary of material modifications, generally due no later than 210 days after the end of the plan year in which the change was adopted; a material reduction in covered services or benefits under a group health plan must go out within 60 days instead.
Getting the real document. Section 104(b)(2) requires the administrator to make the latest SPD, the latest annual report, and the "trust agreement, contract, or other instruments under which the plan was established or is operated" available for examination at its principal office. Section 104(b)(4) goes further: on written request the administrator must furnish copies of those items, and may charge a reasonable amount for the copying. That is the provision that entitles you to the plan document, not merely its summary. The enforcement sits in section 502(c)(1): an administrator who fails or refuses to comply with a request for information it is required to furnish, by mailing it within 30 days, "may in the court's discretion be personally liable to such participant or beneficiary" for a specified amount per day. The penalty is discretionary, it runs per day, and it runs against the administrator personally.
The conflict rule, stated properly. In CIGNA Corp. v. Amara (2011) the Supreme Court held that SPD statements "do not themselves constitute the terms of the plan" for purposes of ERISA's benefit-recovery provision, section 502(a)(1)(B). That much is widely quoted, and it is where most summaries stop. In the same opinion the Court went on to find that "a different equity-related ERISA provision," section 502(a)(3), "authorizes forms of relief similar to those that the court entered" as "appropriate equitable relief," and pointed the lower court on remand to reformation, estoppel and surcharge as the equitable principles it might apply. Stating only the first half tells a participant who relied on a misleading summary that they have no remedy, and that is not what the case decided. The accurate summary is narrower and more useful: the summary does not rewrite the plan's terms, but a materially misleading summary can still be actionable on a different theory.