Thanks.
So really nothing has changed. They have sent a woefully inadequate SAR, so your letter can still go off. It's not as if you're immediately starting court action, they will still have 14 days to get their act together.
I would send the GDPR one before the SAR one, so that in the SAR one you could point out that they are hiding information that you need for ongoing litigation.
All that remains is to decide how much you want to claim for GDPR distress. I know we haven't been much help with fixing the figure. You'd be suing for "distress" which is not easy to quantify. Think of the risks v the gains and have a look at the court fee list I linked to, and when you've decided come back to us.