When the old white button displays first came out, they were the 4/5 voltage. Deere took most of them back and updated them to the dual voltage. I say most because like all product improvement programs, I'm sure there were some that slipped through the cracks.

Some of the older equipment (late '90s and very early 2000s) that used these displays such as pre "NT" 1770 planters and 1900 air carts were using a 4/5 system. Later stuff (think Seedstar Gen. II) went to a 2.5 volt system which is industry standard.