Hi Craig

Nothing to stop you retrospectively reporting something to HSE, though it might raise some eyebrows two years later.

The relevant part of RIDDOR says:

Occupational diseases 8.Where, in relation to a person at work, the responsible person receives a diagnosis of— (a) Carpal Tunnel Syndrome, where the person’s work involves regular use of percussive orvibrating tools; (b) cramp in the hand or forearm, where the person’s work involves prolonged periods ofrepetitive movement of the fingers, hand or arm;

I am going to assume for now that your organisation is the responsible person.

However, diagnosis  is a defined term.

“diagnosis” means a registered medical practitioner’s identification (in writing, where it pertains to an employee) of— (a) new symptoms; or (b) symptoms which have significantly worsened;

So this is not an employee telling you that they have CTS but a medical practitioner setting this out in writing.

.....and probably in this case explaining why it has taken so long to belatedly diagnose the condition, which, in turn would help explain to HSE why your report is delayed.

Worth remembering that making a RIDDOR report is in no way any admission of liability.