hi Nigel
welcome to the forums

google has multiple data centers and sometimes different pages will show up differently based on what data center the search is processed by.
if google has a newer copy of the page then it will propigate through all of their databanks eventually. also one of the indications of an upcomming dance is that sometimes old copies of pages appear.
also google may use different page snippets for different search queries depending on what words are in the search query and on the page.