Can you send the information on the field names? I may then, coronavirus restrictions permitting, try to locate these, as the location is often informative. I'm thinking "wet".
I'd also be interested to know more of the mapping system.
Squares = freshwater sites
Circles = saltwater sites
Diamonds = field names (a series of five names Wilts/Dors/Some)
x = recent names (last century or so)