  Type IIn supernovae (SNe IIn) are a relatively infrequently observed subclass
of SNe whose photometric and spectroscopic properties are varied. A common
thread among SNe IIn are the complex multiple-component hydrogen Balmer lines.
Owing to the heterogeneity of SNe IIn, online databases contain some outdated,
erroneous, or even contradictory classifications. SN IIn classification is
further complicated by SN impostors and contamination from underlying HII
regions. We have compiled a catalogue of systematically classified nearby
(redshift z < 0.02) SNe IIn using the Open Supernova Catalogue (OSC). We
present spectral classifications for 115 objects previously classified as SNe
IIn. Our classification is based upon results obtained by fitting multiple
Gaussians to the H-alpha profiles. We compare classifications reported by the
OSC and Transient Name Server (TNS) along with the best matched templates from
SNID. We find that 28 objects have been misclassified as SNe IIn. TNS and OSC
can be unreliable; they disagree on the classifications of 51 of the objects
and contain a number of erroneous classifications. Furthermore, OSC and TNS
hold misclassifications for 34 and twelve (respectively) of the transients we
classify as SNe IIn. In total, we classify 87 SNe IIn. We highlight the
importance of ensuring that online databases remain up to date when new or even
contemporaneous data become available. Our work shows the great range of
spectral properties and features that SNe IIn exhibit, which may be linked to
multiple progenitor channels and environment diversity. We set out a
classification sche me for SNe IIn based on the H-alpha profile which is not
greatly affected by the inhomogeneity of SNe IIn.
