Hi Rebecca - what's legal or otherwise is not for us to advise or comment on here. That would be a matter for your conveyancer, the developer and Homes E to consider. Provided we get the consent then it's sufficient to register 
Again, whether it should have been picked up is only a Q your conveyancer can answer with regards what checks they made and/or are required to make and at what point they consider exchange and completion can then take place.
Homes E said they would keep me informed re progress at their end but I suspect that will be very similar to how you are also kept informed, namely only when it has been completed for example.