No, it’s just that these US documents always give the most favorable RoF for the guns.
The RoF of guns generally fluctuate depending on the projectile mass and the resulting recoil forces.
The different projectile mass of the MG 151 and 151/20 shells can be substantial.
So while the manual basically gives an average of 700 RPM, the RoF for heavier shells could easily reach 800 RPM.
The MG 151 was generally loaded with more 57g explosive rounds than the 72g AP-T and the MG 151/20 manual has a weight for 20mm Mineshells of merely 86g compared to the shells which were 115g at that time.
The RoF of the MG 151/20 probably slightly increased over time, as the Mineshells got heavier and the other shells slightly as well.
Same story with the Ho-5, which either fired super light 84.5g shells or 123g AP shells, even heavier than the MG 151/20 shells.
So the RoF could be as low as 700 RPM but as high as 950 when firing AP-T.
Of course they only loaded a single AP for every two or three other rounds, so the practical RoF was 800 RPM or lower.