Royal Mail no longer require postal counties on letters. They say you can put whatever county you want on the letter. Postal counties are very inconsistent. Some modern counties are observed, such as Merseyside, whereas Greater Manchester was never introduced as a postal county so Rochdale stayed in Lancashire postal county and Hale stayed in Cheshire postal county.
There was further confusion after 1986 when the Greater Manchester Council was abolished. That led to some people believing that they had returned to the previous pre-1974 counties, whereas in fact they were still in Greater Manchester and there was merely a conversion to unitary authorities.
It has become common practice in recent years for Greater Manchester to become shortened to just 'Manchester', particularly in the media, similarly to how London is now almost never 'Greater London'. I have noticed a lot more acceptance of this usage in the outer areas, particularly in south (Greater) Manchester.
In strict urban area terms, the Office of National Statistics has defined a Greater Manchester Urban Area (not taking into account any administrative boundaries) that includes Hale as there is continuous urban area between Hale and the city centre with no gap in countryside of more than 50 metres.
http://en.wikipedia.org/wiki/Greater_Manchester_Urban_Area
Tickets to Castleton are printed as Castleton (Manchr) even though Castleton (G Man) might be more acceptable to Manchester refuseniks.