Question about Kursk OOB

[bwv]

Comparing the OOB for Kursk with the OOB in the back of the Glantz book, there are some significant differences, for example

Central, Steppe & Voronezh Front - Glantz
1,426,352 Men (combat strength)
27,663 Guns & Mortars
518 MRLs
4,938 tanks & SP Guns

Central, Steppe & Voronezh Front - HPS
579,798 Men
12,785 guns
7,145 vehicles

compared to

AG Center + AG South - Glantz
780,900 men
(Glantz does not list German guns)
2928 tanks and AG Guns

AG Center + AG South - HPS
268,595 Men
4520 vehicles

Note the vehicles are not directly comparable - the Glantz numbers are tanks & sp guns while the HPS numbers are for all vehicles. For example, the XXXXVII Panzer Corps the tank totals are in almost exact agreement between Glantz and HPS. Similarly the 5th Guards Tank Corps is not materially different from Glantz in the number of tanks.

For the Soviets at the individual Army level there is over a 2-1 difference in manpower between Glantz and HPS. The Soviet Rifle divisions tend to be under 4000 men in the HPS oob where a full strength soviet rifle division was about 11,000

My question is the differences in men and guns, is it an issue of game mechanics or something else?