This section covers the share-supply calendar: the recurring, largely known-in-advance events that change how many of a company's shares are available to trade — and what management's own choices about issuing or trading stock signal. Unlike the rest of Flow, Positioning & Dealer Dynamics, which mostly tracks derivatives-driven dealer hedging and mechanical fund flows (gamma, vanna/charm, CTA trend flows, the passive bid, index rebalances), this branch is about the cash equity itself: when fresh shares hit the float, when locked shares unlock, when the corporate "structural bid" goes quiet, and when the people with the most information buy or sell. The core tension running through every node is the same — these are scheduled or disclosed supply/sentiment events whose existence is public, yet markets still react to them, which makes each one a recurring test of how efficiently anticipated supply is priced. The honest summary across the section: the flow mechanics are real and measurable, but the predictable price effects range from small-and-front-run to genuinely contested, so these are best treated as context and risk flags, not standalone triggers.

What this section covers (and what it doesn't)

The unifying question is: "Is the supply of, or the informed demand for, this stock about to change for a calendar/disclosure reason — and what does that imply?" That spans two related families:

• Supply shocks — events that increase (or withdraw) the shares available to trade: lockup unlocks, secondary/follow-on offerings and dilution, and the temporary removal of corporate repurchase demand during buyback blackouts.
• Informed-participant signals — what corporate insiders' own disclosed trading reveals about the supply/sentiment balance.

It deliberately does not cover derivatives-driven flow (dealer gamma, 0DTE, OPEX/quad-witching), systematic fund mechanics (CTAs, vol-control, the passive bid), index rebalance/inclusion supply, or squeeze dynamics — those are the other nodes in this parent section. Float and short-interest interact with supply windows (an offering or unlock changes the squeeze math), so cross-reference those nodes, but their primary treatment lives elsewhere.

Map of the sub-topics

1. Buyback Blackout Windows — the recurring stretch around each earnings release when a company voluntarily suspends repurchases (driven by Rule 10b-5 anti-fraud exposure, not a specific mandate; 10b5-1 plans are the workaround). Corporate buybacks are an enormous, price-insensitive source of demand, so flow-watchers argue a "structural bid" is withdrawn when much of the index goes quiet at once. This is the most contested node in the section: the flow withdrawal is genuine, but the predictable price effect is largely folklore — State Street and CNBC reviews found no reliable negative performance during blackouts, contradicting the popular "buybacks go dark, so sell" narrative.

2. Lockup Expirations — the date (modally ~180 days post-IPO, set by the underwriting agreement) when insiders and pre-IPO investors can first sell, often multiplying the tradable float. The best-studied node empirically: Field & Hanka (2001) document a small (~−1.5% three-day) abnormal return and a permanent volume jump, concentrated in VC-backed, high-run-up names — but the effect is small, front-run, and the existence of any reaction to a known date is itself a market-efficiency puzzle. Weight by overhang-to-float and holder type, not by the date alone.

3. Secondary Offerings & Dilution — fresh share supply from a public company after IPO, hinging on one critical distinction: a primary (issuer) offering mints new shares and dilutes everyone, while a non-dilutive secondary is insiders reselling existing shares (overhang, no dilution). Run off shelf registrations (S-3) via 424B5 supplements, ATM programs, RDOs, PIPEs, and — at the microcap pathology end — toxic variable-rate convertibles ("death spirals"). The announcement-day drop is robust (Eckbo-Masulis-Norli put it near −2% to −3% for US industrials), explained by Myers-Majluf adverse selection; the multi-year SEO underperformance (Loughran-Ritter) is real in the data but its cause (mispricing vs. risk) is genuinely disputed.

4. Insider Buying & Selling — Section 16 officers', directors', and 10%-owners' disclosed open-market trades (Forms 3/4/5; Form 4 within two business days post-Sarbanes-Oxley). The signal is deeply asymmetric: buying — especially opportunistic open-market cluster purchases (code P) — carries real but modest predictive content (Lakonishok-Lee; Cohen-Malloy-Pomorski's "opportunistic" subset ~82 bps/month), strongest in small-caps; selling is mostly noise (taxes, diversification, 10b5-1). A months-long horizon, not a swing trigger.

When this section matters — and when it doesn't

It matters most for: small- and micro-caps (where forced dilution and toxic financing are frequent and deep), recent IPOs inside their lockup window, names spiking on a clinical/contract catalyst (the canonical overnight "sell-the-news" raise), and high-conviction theses where insider cluster buying confirms management agrees the stock is cheap. In these, the supply read is a genuine, recurring edge.

It matters least as a market-timing tool for large, liquid, profitable names. The aggregate "% of the index in blackout" overlay is the section's most over-traded folklore; the lockup "always dump" lore overstates a small front-run average; and raw "insider selling" totals are dominated by benign mechanical events. Across the board, these are averages and context, not tradable point estimates for any single name, and on the actual event date they are routinely swamped by earnings, broad-market regime, and idiosyncratic news.

Sources

• Per-node primary sources (verified in each child doc): Field & Hanka (2001, Journal of Finance) and Bradley et al. (2001) on lockups; Asquith-Mullins (1986), Masulis-Korwar (1986), Loughran-Ritter (1995), Eckbo-Masulis-Norli (2000, 2007) on SEOs; Lakonishok-Lee (2001) and Cohen-Malloy-Pomorski (2012) on insider trades; State Street SPDR (Bartolini-Kaplanian) and CNBC (2018) on buyback blackouts.
• Regulatory framework: SEC Rules 10b-5, 10b-18, 10b5-1 (incl. Dec-2022 cooling-off amendments), Rule 144/701, Section 16 Forms 3/4/5, shelf registration (Rule 415 / Form S-3).
• StockCharts/Investopedia/practitioner references (DilutionTracker, StrikeRates, Mayer Brown, Harvard Law Forum) as cross-checks.

Disputes flagged at section level: the buyback-blackout price effect (real folklore-vs-measured conflict — Goldman desk framing vs. State Street/CNBC null results); the lockup reaction's compatibility with market efficiency; and the cause of long-run SEO underperformance (mispricing vs. risk/liquidity). The announcement-day SEO drop and the insider-buying signal are the most robust claims in the section.