The AT value of 4 was originally for HEAT rounds (well, it was originally 4-7 but this got downgraded to 4-4 very early on). One could dig through the piles of CSW posts from the early 2000's if they really want to track the debate, but a bit of trawling through webarchive was interesting.
The original daily content on the PZIV included the following:
" Even with the short 75mm L24 cannon, the PzKw IV could destroy enemy tanks using hollow-charge rounds. These became available in the summer of 1941 in both Russia and North Africa. As almost all
Panzer Grenadier scenarios issued to date that include PzKw IV tanks take place after this superior anti-tank ammunition became available, the PzKw IVE has a misleadingly high anti-tank value of 4, reflecting use of this round. Future games based on the Polish, French and Balkan campaigns of 1939 through 1941 will show the tank with a much lower anti-tank value."
You can see it here
https://web.archive.org/web/200812292207...PzKwIV.php
Funnily enough the new daily content article that replaces the original trims that down to:
" Even with the short 75mm L24 cannon, the PzKw IV could destroy enemy tanks using hollow-charge rounds. These became available in the summer of 1941 in both Russia and North Africa."
http://www.avalanchepress.com/PzKwIV.php
Intentional change? Embarassing oversight noticed when republishing the article?
Couldnt tell you.