COS start date changed

[Dasistfact]

This April as per new guidance start date amendment was clarified with the following words:Certificate of Certificate of Sponsorship Start Date

The U.K. government recently sought to restrict the length of time a Tier 2 sponsored migrant’s start date can be delayed from the date originally declared on the CoS to a maximum of four weeks.

KPMG NOTE

As it was possible to interpret the new rule in different ways, the government has now released further guidance to eliminate any ambiguity.

Not More Than Four Weeks after Original Start Date

The start date stated on a CoS must be the date that a migrant will start working for a sponsor in the United Kingdom. Under the Immigration Rules, a migrant can be granted entry clearance no more than 14 days before the start date given on the CoS.

It is now clear that once the entry clearance visa has been granted, it is possible to delay the original start date but, in the case of a Tier 2 (General) migrant, any revised start date cannot be more than four weeks after the original start date stated on the CoS.
Does it mean that all CoS amendments in all CoS issued or only those that were obtained after April 2017?
If someone's start date was delayed by 8 weeks in 2016, does it mean that there will be issues with ILR and extension?