Many of the decal patters were used with specific models, and some with only a few. Red Eye and Lotus were only used on the 66 Model.
So if you say "Red Eye" Singer, collectors are going to know it's a 66. though I've had some call the LaVincedora a "red eye" - but then I've also had some refer to a 128 as a 66 . . .
this part of ISMACS lists the common models the decals were used on.
http://ismacs.net/singer_sewing_mach...ic-decals.html