There is an inaccurate statement in this catalog item.
It says: "The top of the heads of the earliest examples of this part had
a more squared-off forehead."
It should be "...some of the earlier examples of this part...".
The first heads in 1978/79 were not squared off, it was something that happened
roughly in the mid-80s (and possibly later) and was possibly a North American
manufacturing "thing". I know this from collecting many sets (European,
US and Canadian) from 1978 onwards. I have only come across these in Canadian
sets where I know it was "original". It could be they were manufactured
in the US for a brief period of time.
There hasn't much informed discussion about this but based on what I know
and what have read the catalog statement is definitely inaccurate. Collectors
of early sets will be misled into getting the wrong heads if they believe the
statement.