I will not comment further on the numbers of Prussian infantry regiments.
Jany mentions `Hutbueschel` for each of the Saxon infantry regiments taken into Prussian service in 1756.
`Hutbueschel` means `hat pompon` i.e. tricorns.
If they had been fusiliers (which Jany does not say) they would have worn fusilier caps and Jany would have called them `Muetzenbueschel` (cap pompons) which he explicitly does not.
I thus maintain that these Saxon regiments were musketiers.
You still have not given your sources for them being fusiliers; is it Duffy?
Have fun with your new daughter.