I would like to depend on Biosample database for sample metadata rather than SRA. Do all SRA samples have a corresponding sample in Biosample? I've browsed a handful of studies, and found that they do. However, I'm wondering if anyone knows better than I.
I know that samples submitted to NCBI are regularly pulled into BioSamples by Ensembl. I'm not sure if that happens in the other direction.
Check this directory for SRA reports. I would look at the datalist directory to see if those files help.