As Donald says the answer to both is no. It's not complex so extension doesn't apply.
None of ICO's examples are really relevant.
They are probably right but I can see why you think not clear if not explained.
manifestly unfounded or excessive : the answer here is to refuse or levy a charge, not to extend although I guess an excessive request could also be complex too so in theory you could ask for a fee and say "if you pay it will take three months"
an exemption applies - probably right for most exemptions but if you count taking out third party data (especially mixed data where you may have to go through documents line by line) as an exemption that can be very complex
you are requesting proof of identity before considering the request: not complex but extension not really relevant. Although not as clearly spelt out as under DPA98 I can't see that you have a valid request until you are reasonably satisfied on identity so time not running anyway. As in first case it could be complex too.
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