The Dolnet Universal
These are a slightly less elaborate version of the M70: it doesn't have an offset bell and has different engraving, but otherwise appears identical to the previous model.
I have heard of altos and sopranos in this serial number range.
As far as I have been able to determine, this is the last model Dolnet. If the M70 was introduced in 1970, I see no reason not to believe that these horns were introduced in 1980.
Bb Tenors
s/n unknown
Silver Plate
Thanks to David Hughes