Did you mean the size of the house as in square footage? The MPAC assessment is based on your square footage, lot size, amenities (e.g. a solarium or a swimming pool) to gauge your property tax amount. The more improvement you have the more tax you will have to pay. So, if I were you, I would not report/correct the info with MPAC, because the more square footage you claim, the more your property tax will be.
If your question was whether the 1450 or 1350 sq ft is the correct area, I would call the original builder and ask for the square footage of this particular model.
I'm not sure if that helps, please let me know.