So I've just got out of a meeting with the company, and it has taken another twist.
So its looking like there were never AVC's to begin with. When payroll company changed in Jan 2012 my pension contributions were mislabeled as AVC's. There is only an AVC entry and no Employee entry. The value matches my % contributions. In 2011 and before they were labeled correctly as Employee Pension contributions.
However mid 2014 the labeling was corrected to be employee contributions, but a duplicate avc entry remained. The avc value never increased from that point on, but the contributions did.
So it looks to be a payroll only issue, and it started in 2014 not 2012 like first thought. The meeting with the broker in Jan 2012 seems to be a red herring as it coincided with payroll changes.
Shortfalls is down from 17.5K to 10K.
I have looked through my payslips and all this seems to match. The only way its the bigger of the two was if I had set up and AVC to match my standard contributions and it was messed up from there, but, me, the broker and employer have no record, so it may have been a previous employment that has me doubting.
I should have a better handle on it either way.