Herts is short for Hertfordshire - a different place altogether. I have never seen Herefs as an abbreviation for Herefordshire. I am sure that if you were addressing an envelope you would put 'Hereford' where the county would go. I have an old book (1947) that lists all the counties of the UK. Some have since dropped the -shire. Devonshire, Dorsetshire, Flintshire for instance.
emeritus I can assure you that Hereford does exist and so does Worcester. The administration of the two councils was amalgamated but the cities exist and so do the seperate counties!