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ESA is an indefinite award with regular reassessment, the normal time for reassessments in the SG is three years so you have been lucky not to have received a form before.
This is a full review of your form so you need to complete the form in detail and provide evidence in support as you can. Please use our latest ESA Claim guides, although the Descriptors have not been changed, there have been a number of updates to the DWP guidance since you were last assessed.
www.benefitsandwork.co.uk/help-for-claimants/esa1 Gordon