The old model valued holdings in ADJ (total-return index) units but
computed distribution flows as raw per-share dollars — so every
distribution, and its tax, was overstated by the raw/adj ratio
(JLPSX: 30.10/11.25 = 2.7x; the Dec-2020 cap-gain tax showed as 12.1%
of the account instead of the true 4.5%). The wiggle in the after-tax
curve was this bug, not a convention issue.
tax.py now:
- values holdings in RAW share units on close prices (bundle.close);
- receives the per-share distribution on its event date, pays the tax
(recorded in TaxResult.taxes), and reinvests the after-tax remainder
at the same day's raw close — the tax's effect lives in the (smaller)
reinvested units and is NOT also deducted from cash (double-count
caught and fixed in review);
- recomputes market value after the reinvestment so equity[t] is the
post-event liquidation value.
With the fix, the 'as-if-liquidated' equity on JLPSX's ex-div day drops
by exactly the true tax cost (4.72% vs 12.1% before); the -22.9% price
drop is offset by the distribution kept.
Also:
- app.py passes bundle.close to the after-tax model (pre-tax
portfolio_returns still uses adj);
- JLPSX/JLPYX: the 2020-12-11 6.824 capital-gain distribution is moved
to the true ex-div date 2020-12-14 (remove/add correction ops), so
the reinvestment prices at the post-drop close;
- tests/test_tax.py: 8 synthetic regression tests (tax magnitude,
reinvestment MV, no double-count, ex-div equity step, per-component
rates); run_tests.sh now runs it.
JLPSX showed a bogus +29.3%/-22.9% 3-day wiggle in Dec 2020: Yahoo dated
the 6.824 year-end cap-gain distribution on the 12-11 record date but the
market went ex-div on 12-14 (close 30.10 -> 23.22), so the raw Adj Close
column pre-applied the adjustment 3 days before the price actually fell.
New 'history' correction op ({date: {col: value}}) patches individual OHLC
cells at bundle assembly (full build, incremental, and correction-changed
recompute paths); check_corrections validates dates/columns; 4 new tests.
scripts/scan_adj_misalign.py finds the artifact set-wide: 481 hits on 278
symbols, overwhelmingly December year-end distributions of value funds
(JLPSX's class of fund). scripts/fix_adj_misalign.py repairs it
arithmetic-only (rescale adj in [event, ex-div) by (1-f); cumulative
returns unchanged, cross-checked implied dist vs the price drop). Applied
to the only curated-fund hit (JLPSX) and its sister class JLPYX (implied
dist 6.824 both = official amount; ex-div 2020-12-14). The remaining ~276
symbols are reported in reports/adj_misalign/scan.md for a bulk run.
Yahoo changed the shape of its event feed between downloads: a 2026-08
re-download of CVIX/JLPSX shows it no longer returns capitalGain events at
all (the dividend stream still carries the year-end rows), while stale
tickers now return no events at all. File-specific remove ops therefore
break silently on the next re-download, so the double-listing fix is now
expressed as layout-agnostic invariants applied at bundle assembly
(idempotent, hold for full and incremental builds):
dedup: [[date, amount]] keep at most one copy of a same-date/
same-amount cross-file pair (the capitalGain copy when both present)
drop_capg_copy: [date] the capitalGain row on that date is the
spurious copy of the dividend row
- data.py: apply_invariants() at bundle assembly + pure dedupe_event_rows()
shared with verify_official and tests (8 new test cases, 22 passing)
- JLPSX/CVSIX corrections rewritten with the invariants (2019-08-08 now
keeps the dividend amount per the verified same-date pattern)
- scripts/scan_double_listing.py: whole-dump sweep -> reports/double_listing/
6,421 symbols scanned: 1,218 with same-amount pairs (6,589), 1,631 with
differing-amount pairs (12,366, reported only - not distinguishable from
legitimate same-day div+capg without per-fund official data), 83 with
repeated within-file rows (ingest keep-last already collapses them)
- scripts/apply_dedup_corrections.py: bulk 'dedup' corrections for the
1,218 same-amount symbols (1,212 new files; the 6 verified funds keep
their explicit, official-verified corrections)
- scripts/check_corrections.py: integrity check for every correction op
against the actual (frozen) files - caught a mis-filed CVSIX entry
