FOI - Affordable housing statistics [June 2020]

Over the past four years, the GLA has reported 51,771 affordable homes started; but just 25,608 completed. Year after year, homes that appear in the 'starts' fail to appear subsequently in the completions.  This is a new pattern, which did not appear before 2016 in London, and does not appear in the comparable national affordable housing statistics.

Please can you help me with an explanation:  

 Q1 How many homes are 'started' when one shovel is stuck into the ground.  Just one home?  All of Phase One of a development?  Or hundreds of homes on a complex scheme that may take decades to deliver?  There may be much potential ambiguity here.  Can the reporting system be better regulated to avoid mis-counting starts?   

Q2 Perhaps delivery is taking longer because of funding gaps. Maybe there are ‘false starts’, where a shovel is put into the ground and an online form filled in, while actual delivery cannot go ahead because funding is not in place.  What action can you take to drive any 'false starts' out of the reporting system?

Q3 Please can you comment on why some tenures are further behind on delivery after being started: Social Rent and London Affordable Rent, and shared ownership are more than 50% behind; while market housing (funded by affordable housing grant) and Affordable Rent (above LAR rates) appear to be completing in full.  Perhaps some homes started as Social Rent or LAR are being delivered as Affordable Rent. Is there anywhere that these changes of tenure are reported in the GLA’s planning control system?