I'm pretty sure that for any HSC task you have to be given proper notice and everything-> given that you just found out that it counted, then I would think that what the school did wasn't allowed. Call BOS and see what they think. Also, why are your trials weighted at 50% if you've got 4 assessments all together? I thought our MX2 trials were heaps important at 45% but we only had 3 assessments so its weighting had to be big
The only reason I can think of is that your school is treating the 'MX1 yearly' as not your year 11 stuff but really a HSC assessment that will take place this term (so really start of year 12 but in terms of actual school years, still year 11)