Gallery housed too much, until now (6)

I believe the answer is:

todate

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

'gallery housed too much' is the wordplay.
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'housed' means one lot of letters goes inside another.
'too much' becomes 'od' (abbreviation for overdose).
'tate' placed around 'od' is 'TODATE'.

Can you help me to learn more?

(Another definition for todate that I've seen is " Until this moment".)

I've seen this clue in The Daily Express.

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