Informed study backing block of, say, ninety-nine shares (3,3)

I believe the answer is:
odd lot
This could be a double definition.
'informed study backing block of' is the first definition.
I can't judge whether this defines the answer.
'say ninety-nine shares' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Another definition for odd lot that I've seen is " block of shares".)
I've seen this clue in The Times and The Sunday Times.
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