I understand what you are saying but in merger or acquisition scenarios, institutions might build positions in the stock as part of the deal process, and disclosure may be delayed avoiding influencing negotiations or revealing sensitive information.

13F Filings in the U.S.:
Institutional investment managers with over $100 million in assets under management must disclose their holdings quarterly in a Form 13F to the SEC. This means there could be a delay of up to 45 days after the end of the quarter before the public learns of the purchases.

13G or 13D Filings:
When an institution acquires more than 5% of a company’s stock, they must file a 13G or 13D. A 13G is for passive investors and can have up to a 45-day delay, while a 13D must be filed within 10 days of crossing the 5% threshold.