Subdivision – Green titles vs strata

We have started our first subdivision and through our surveyors we applied for four green titles. Our plumber now thinks the sewer line may be too deep for green titles (roughly 5.5 m deep)  and that we may have to reapply for strata titles. We do not have a plumbers kit as yet though. As I understand it this means we have to go back to the beginning of the process – another three months.  This is a costly mistake. My question is should the surveyor have picked this up in the beginning and advised us? Any advice would be much appreciated. Michelle