I'm trying to establish if there's any difference between helmets issued by Avon & Somerset and Gloucestershire from late 1970s to late 1980s - can you help? A&S have used single screw helmet plates since the late 1970s. I've seen an early 1980s Glos with plastic HP and rose top which A&S also used at the same time. I'm looking for any detail which would help distinguish between these helmets if they didn't have the HP to confirm which they were.