XLE☆

Membership changes are brackets, not dates. Adds and drops are the set difference between this book and the fund's PREVIOUS book on the same leg, over the positions whose identifier resolved. A book is a snapshot at the issuer's own period end, so the index change happened somewhere between the two snapshots — the pair of dates is the answer, never a single effective date.

An identifier-mapping change is not an index change. A candidate add is cross-checked against the PRIOR book's unmapped positions (and a candidate drop against the NEXT book's) by normalized issuer name. A hit is reclassified 'identifier mapping' — the fund held the position in both books; only our ability to resolve its identifier changed. Measured live, 12 of SPY's 140 raw adds are this class (General Electric, Linde and BlackRock among them), so an unadjudicated diff prints index events that never happened. The check is a NAME comparison, so it cannot catch a rename that changed the name too: L Brands became Bath & Body Works in 2021 and still reads as an add and a drop, because the two books disclose two different companies and the identifier that would bridge them (the CUSIP changed with the rename) is not in our reference data.

Every book discloses its own coverage. Each book discloses the positions whose ISIN/LEI did not resolve to a served symbol. They are listed with the filing's own name and weight — a book that leaves part of its portfolio unmapped can under-state a small position and cannot contribute to the members table.

Turnover counts names. Name turnover = (adds + drops) ÷ 2 ÷ the prior book's holding count — a one-way count of NAMES, not weight: a book diff carries no trade, so a weighted turnover would be invented.

Fundamental columns are today's.

Source: SEC N-PORT position books (public domain) (27 books, 2019-09-30 → 2026-03-31) + SEC Form N-Q / N-CSR Schedules of Investments (reconstructed) (24 books, 2013-03-31 → 2019-03-31).