The first of March; diary's changed lots (7)

I believe the answer is:

myriads

I'm a little stuck... Click here to teach me more about this clue!

'lots' is the definition.
The answer and definition can be both quantities as well as being plural nouns.
Maybe they are linked in a way I don't understand?

'the first of march diary's changed' is the wordplay.
'the first of march' becomes 'm' (1st letter of 'march').
'changed' is an anagram indicator.
'diarys' with letters rearranged gives 'yriads'.
'm'+'yriads'='MYRIADS'

Can you help me to learn more?

(Another definition for myriads that I've seen is " huge numbers".)

I've seen this clue in the Sydney Morning Herald.

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