Not many dwelling from that era can satisfy the EPC rating B, like your aunt's. On https://assets.publishing.service.gov.uk/government/uploads/system/uploads/a

Not many dwelling from that era can satisfy the EPC rating B, like your aunt's. On https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/207196/20130613_-_Hedonic_Pricing_study_-_DECC_template__2_.pdf https://assets.publishing.service.gov.uk/government/uploads/... , on page 13 you can find the distribution of EPC ratings by age.