Thanks. I did some research and found (as you said that rules do allow the extension of PBS Dependent):
Change to the Immigration Rules: 9 July 2012
From 9 July 2012, dependent partners of PBS migrants must complete a five year
probationary period before they qualify for ILR. If the PBS migrant obtains ILR or British
citizenship before their partner has completed their 5 year probationary period,
the partner
can still apply for further leave to remain as a PBS dependant rather than as the partner of a
settled person. If their application meets the requirements, leave to remain can be granted
for up to 3 years.
Hopefully that'll clear the air a bit for myself and others who are confused