Meyer-Griffiths never served with any of the regular battalions of SWB. He was a part-time volunteer officer (joined in 1898), later schoolteacher and respected historian. The only AZW veteran he might have spoken to was Alfred Sale who was RSM and QM of 3rd Volunteer Battalion when Meyer-Griffith joined this battalion. Sale was 25B/2080 Sgt Sale, A who joined 1/24th (from 50th Foot) after being on the draft on transport Clyde which arrived in Dundee on 1.5.1879 following the disaster at Isandlwana.
So Meyer-Griffiths' account from Sale was 2nd hand. However he could have spoken to 25B/1395 Pte (then Sgt) Williams, J VC, 3 (V) Battalion SWB who was RD but not Isandlwana. I suspect Meyer-Griffith's account was probably from what he had read, such as 'The Historical Records of the 24th Regiment' published in 1892. So I cannot see that it would have revealed something we did not already know.