Messy Nell ignored health plan revision for ulcer (6)

I believe the answer is:

aphtha

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'revision for ulcer' is the definition.
I can't tell whether this definition defines the answer.

'messy nell ignored health plan' is the wordplay.
'messy' indicates anagramming the letters.
'ignored' suggests deleting specific letters.
'health'+'plan'='healthplan'
'healthplan' with 'nell' taken away is 'hathpa'.
'hathpa' with letters rearranged gives 'APHTHA'.

Can you help me to learn more?

(Another definition for aphtha that I've seen is " evidence of complaint".)

I've seen this clue in The Hindu.

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