When you say 'as far as numbers go' it means 'considering everything/considering what we are talking about.' Yoi can say it about anything. For example- 'hes not that big, as dogs go.' Or 'he's not that expensive, as houses go'. So, it acknowleges that it is not expensibe for a house. It could be expensive for a watch. 'All that' means very. 'Its not very accurate'

We may not be as exact because the actual numbers change