IIRC, dont take my word for this,
Kar98a, a stub nosed carbine with a flat bolt handle used turn of the century till about end of WW1, would evolve into the AZ variant.
Kar98AZ, looks more like the k98k to come had distinct staking hook, "normal" rifle lenght. 'normal' 8mm amunition. Also, the polish version of this rifle is the only true K98 rifle.
Kar98b, is a Gew98 with the K98k sights, the rifle used from the 1920's onwards in Germany before the k98k came.