Rock bottom? Well, I'm a lot different (3-4,3)

I believe the answer is:

all-time low

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'rock bottom?' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'well i'm a lot different' is the wordplay.
'different' indicates an anagram.
'well'+'im'+'a'+'lot'='wellimalot'
'wellimalot' with letters rearranged gives 'ALL TIME LOW'.

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I've seen this clue in The Telegraph.

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