https://www.slab.org.uk/guidance/submission-of-diagnostic-advice-and-assistance-accounts-timebar-after-three-months/
You must send us a diagnostic account within three months of the date of conclusion of the advice and assistance. Whatever the value of the account, and notwithstanding any further work which you may carry out, we will not pay any supplementary account.
We have no discretion to accept a late diagnostic account.
This has to be a detailed account.