Sheaffer models are particularly vexing to identify, since not only do they not imprint the pen itself with a name, but the differences between contemporary models can be quite small.
These pictures are arranged in historical order. They don’t represent every pen Sheaffer ever made, just the ones I’ve had a chance to examine. There is a similar resource, of slightly greater breadth if of rather more commercial thrust, available through Peyton Street Pens; if you can’t find what you seek here, you may well find it there.
Flat tops (1913 – c. 1929; hard rubber until 1924, celluloid after that date)

Balance (1929 – c. 1942)
Tuckaway (1940 – c. 1949)
Triumph(1942 – c. 1948)
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- Triumph (the original model)
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- Valiant (note: two band widths; clip is hidden in second image, but is present)
Early Touchdown (so-called fat models) (1949 – 1950)
“Thin Model” Touchdown (1950 – 1951)
“Thin Model” Snorkel (1952-1959)
TipDip (1953 – c.1963)
PFM (1959 – 1968)

Cartridge (1955 – c.1997)

Skripsert (1955 – ?) (Not so much a model name as a description of the filler)

Stylpoint (c. 1957 – ?) (General descriptive also, referring to semi-hooded appearance)

Target (1960 – 1961)

Compact (1961 – 1962)
Imperial and all its lineal descendants (1961 – 1998)
“Dolphin” (1962 – 1964)

Lifetime(1963 – 1964)
Stylist (1966 – c. 1968) Also appears with small Triumph point– see Imperial II above for example

NoNonsense (1969 – c. 2003)

Targa (1976 – 1998)

S-Range (Early to mid-1980s)

Targa Slimline (1982 – 1998)
Sentinel (c. 1989)

Fashion (1990 – 2002)

Award (1995 – c. 2003)

Legacy (1995 – present)

School (c.2000 – present?)

Javelin (2001 – c. 2009)

Agio (2002 – present)

Viewpoint (c. 2003 – present)

100 (c. 2009 – present)

300 (c. 2009 – present)

VFM (2011 – present)

Taranis (2013 – present)
