I wasn't making assumptions that no-one else would enter the...

I wasn't making assumptions that no-one else would enter the buying. That would hardly be realistic. I'm simply saying that if what appears to be a major buyer of a stock stops buying then the price is likely to be lower than if they had kept buying. Note that "Directors Interest", which VinP originally commented on, concerns MG buying on his own account, which does not affect NTA. The buying back of shares you mention is another matter.

I probably should add that my data base targets are based on end of month figures as this is the only time historically for which most LICs published NTA. Trying to calculate daily NTAs from portfolio individual stock (when they're known) prices for multiple LICs is way too much for me. With the current trend to give weekly and, for some LITs even daily, NTAs, it could be feasible to eventually target on that basis once sufficient weekly / daily data has been accumulated.