Once again, thanks for the useful info. Moving the photos to another hard drive as separate years seems to have solved the problem.
Replying to the remark on wiping the drive regularly.
It seemed to be common in years gone by. In the days of DOS 6.22 I never had the need, but the various Windows versions I went through it was an easy process to carry out and the improvement was marked. Drives were small, wipe was quick, and end up clearing the Master Boot Record as well.
I could have everything up and running in two hours.