Dave Judson's Cave Studies series booklet is available at CS18 if you have membership of BCRA. If I have it correct, although Simpson died in 1962, his housekeeper who was the main beneficiary of his will, remained in the house in Commercial Yard. Miken's extract of Dave Judson's booklet shows the material was still in that house in 1971. I guess the presumption is that the material did not move onwards until 1973. But is there any written confirmation of that?
We know that the material was there in October 1971, as Ian Plant, the then Recorder of the BSA was suggesting removing it to the Craven Museum. This idea was considered, and according to the next BSA Bulletin, published in February 1972, rejected. The Secretary's report published in September 1972 makes it clear that the records were still on the premises at that time. I understand that the records were not mentioned in the final two Bulletins.
In the February 1974 BCRA Bulletin, Peter Haigh, the BCRA Librarian, in his report states: “The Duke Street premises in Settle, which formally housed the BSA records and possessions, have now been vacated. The British Periodicals have been transferred to Halifax and these and the whole of the former CRG library are available on postal loan. The remainder of the material has been transferred to the Craven Museum in Skipton.”
The “remainder of the material” were the 100 volumes now in the care of the BGS. They didn't stay at the Craven Museum for very long for reasons of security, and were transferred to Tom Lord's house in Settle who was their custodian for the "late 1970s - early 1980s" (to use his words). Following that, they were transferred down to Derbyshire, where they had a similar peripatetic time until their transfer to the BGS in August 2009.
So to answer your question, Bob, all currently available evidence points to them having been moved from Commercial Yard to the Craven Museum in the last half of 1973.
Jenny Potts and Mary Wilde are working through the BCRA minutes etc. to clarify their travels for the 1980s onwards.
It's a rather sad saga, which has being on-going for forty years. It is good that these valuable records are being properly cared for by the BGS, but currently, there is no easy way to see what is in them. From a personal point of view, I am really hoping that any obstacles preventing their digital images being made more widely available will be overcome.