The owner could have gifted a small interest in the company
to each daughter, grand-daughter, and perhaps their spouses
in each year of those decades, letting subsequent value growth
and inflation accrue to the surviving family members.
And also, perhaps transformed the company ownership structure
into a limited partnership as well, claiming a lower market value
for the shares owned by limited partners.
tl;dr: First rule of US estate planning: Die broke.
This is exactly what should have been done, but requires a longer term commitment, as well as releasing _some_ control while still alive. (both of which I think are a good thing in context)
Note especially the discount from fair market value
for shares of interest in an FLP.
[usual disclaimers - not a lawyer, not legal advice,
see a qualified professional in your jurisdiction, etc.]
The problem with tax/estate planning is the same problem as insurance
- the time when you really want to have done it
is often the time when it is too late to get it.
(e.g., founder/owner is dying, building is flooding or on fire, etc.).
And also, perhaps transformed the company ownership structure into a limited partnership as well, claiming a lower market value for the shares owned by limited partners.
tl;dr: First rule of US estate planning: Die broke.