hey mate, just to provide some further input into your thoughts on holders etc. I apologise upfront if you know all of the following, but from your post here and on the other (top20) thread it would appear otherwise, just by the context of the phrases you are using.
What you are trying to piece together is exceptionally difficult from the data alone you are using.
You make a few references to broker data and then list the most active - these are stock volumes traded by execution brokers which are market participants that execute trades on market (with each other) and in some cases clear and settle trades. They act for many different clients both retail (mums & dads and sophis) and wholesale (instos, funds, other professional investors/traders).
Market services, such as custody/nominee services, clearing and settlement, research, registries (although usually separate to the rest) are either in some cases separate entities completely or effectively different divisions of investment banks.
Pershing, for instance (NOT Pershing Square, hedge fund, totally different animal) is very active in this space and is owned by BNY Mellon. CS, HSBC, RBC (Royal Bank of Canada) etc.. nominee names speak for themselves...
Many of the investing instos, funds, traders use custody services to outsource the administration of their holdings or be a little opaque as to their identity on the register. These investors may well use the execution broker associated with the IB that owns and runs the nominee company they also use - but by no means always and in many cases these intos use multiple brokers to execute their business because it makes good sense in terms of maintaining relationships and trying to keep them honest(! now there's an interesting concept) especially if you have a lot of business to execute.
To further complicate the issue, many of these IBs still have desks which market-make in stocks, and have proprietary trading desks where their trades are self-executed. By monitoring the broker data you'll get an impression as to who is doing what and when, but not necessarily for whom, either themselves or for their clients (or who their clients actually are).
The best bet (for movements) would be to follow the top holders lists regularly to see the movements (it's public data and you can access it for free if you physically turn-up and ask to see it, but it will start to cost you money if you want them to send you regular data or anything more than a random Top20 as the registries charge for producing lists) but that won't necessarily tell you who the underlying holder/beneficial owner is either (just the 'headline' named holder) - again, there are market services companies that can give you transparency on those things, which they do regularly for the companies themselves, but they charge for it too.
Apologies for the long post, but 'broker data' is frequently quoted on these threads in the wrong context...
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