If I had previously attended a HR-related training or education, can it count towards the 150-hours of HR-related training or education?

Yes. As long as you have evidence of having previously attended a HR-related tertiary education (i.e. HR degree/diploma); or HR-related courses, workshops, conference and seminars accumulating to an aggregate of 150-hours, it will count towards the requirement of the 150-hours of HR-related training or education.