“[W]here a plan does not provide for its own fiduciaries to make a determination of disability — but instead defers to the determination made by the administrator of another plan (like the employer’s long-term disability plan) — then only the terms of the other plan need to be amended. Examples include health plans that extend eligibility, or deferred compensation plans that provide accelerated vesting, to claimants who are receiving benefits under the employer’s long-term disability plan or Social Security Disability Insurance (SSDI).”  Katten Muchin Rosenman LLP