A low-dispersion Keck I spectrum of SN 1980K taken in August 1995 ( t = 14.8 yr after explosion ) and a November 1997 MDM spectrum ( t = 17.0 yr ) show broad 5500 km s ^ { -1 } emission lines of H \alpha , [ O I ] 6300,6364 Å , and [ O II ] 7319,7330 Å .
Weaker but similarly broad lines detected include [ Fe II ] 7155 Å , [ S II ] 4068,4072 Å , and a blend of [ Fe II ] lines at 5050–5400 Å .
The presence of strong [ S II ] 4068,4072 Å emission but a lack of [ S II ] 6716,6731 Å emission suggests electron densities of 10 ^ { 5 - 6 } cm ^ { -3 } .
From the 1997 spectra , we estimate an H \alpha flux of 1.3 \pm 0.2 \times 10 ^ { -15 } erg cm ^ { -2 } s ^ { -1 } indicating a 25 % decline from 1987–1992 levels during the period 1994 to 1997 , possibly related to a reported decrease in its nonthermal radio emission .

A May 1993 MMT spectrum of SN 1979C ( t = 14.0 yr ) shows a somewhat different spectrum from that of SN 1980K .
Broad , 6000 km s ^ { -1 } emission lines are also seen but with weaker H \alpha , stronger [ O III ] 4959,5007 Å , more highly clumped [ O I ] and [ O II ] line profiles , no detectable [ Fe II ] 7155 Å emission , and a faint but very broad emission feature near 5750 Å .
A 1997 HST Faint Object Spectrograph , near-UV spectrum ( 2200 – 4500 Å ) shows strong lines of C II ] 2324,2325 Å , [ O II ] 2470 Å , and Mg II 2796,2803 Å along with weak [ Ne III ] 3969 Å , [ S II ] 4068,4072 Å and [ O III ] 4363 Å emissions .
The UV emission lines show a double-peak profile with the blueward peak substantially stronger than the red , suggesting dust extinction within the expanding ejecta ( E [ B–V ] = 0.11 - 0.16 mag ) .
The lack of detectable [ O II ] 3726,3729 Å emission together with [ O III ] ( 4959+5007 ) /4363 \simeq 4 imply electron densities 10 ^ { 6 - 7 } cm ^ { -3 } .

These new SNe II-L spectra show general agreement with the lines expected in a circumstellar interaction model , but the specific models that are available show several differences with the observations .
High electron densities ( 10 ^ { 5 - 7 } cm ^ { -3 } ) result in stronger collisional de-excitation than assumed in the models , thereby explaining the absence of several moderate to strong predicted lines such as [ O II ] 3726,3729 Å , [ N II ] 6548,6583 Å , and [ S II ] 6716,6731 Å. Interaction models are needed that are specifically suited to these supernovae .
We review the overall observed range of late-time SNe II-L properties and briefly discuss their properties relative to young , ejecta dominated Galactic SNRs .