In the UK, ATCOs are required to add 'millibars' after a pressure setting, whenever the value is less than 1000mb - (the reason is an attempt to avoid confusing pilots who also regularly use pressure settings in 'inches'). One way of ensuring that 'millibars' is specified when required, is to always say it, even when the pressure is 1000mb, or more.
I would also add that:-
"Descend 9000 feet .........."
Could also be ambiguous, hence:-
"Descend to
Altitude 9000 feet, QNH 999 millibars"