  For the last two decades we have been observing a huge increase in
discoveries of long-period comets (LPCs), especially those with
large-perihelion distances. We collected data for a full sample of LPCs
discovered over the 1801-2017 period including their osculating orbits,
discovery moments (to study the discovery distances), and original semimajor
axes (to study the number ratio of large-perihelion to small-perihelion LPCs in
function of 1/a-original, and to construct the precise distribution of an
1/a-original). To minimize the influence of parabolic comets on these
distributions we determined definitive orbits (which include eccentricities)
for more than 20 LPCs previously classified as parabolic comets. We show that
the percentage of large-perihelion comets is significantly higher within Oort
spike comets than in a group of LPCs with a<10000 au, and this ratio of
large-perihelion to small-perihelion comets for both groups has grown
systematically since 1970. The different shape of the Oort spike for
small-perihelion and large-perihelion LPCs is also discussed. A spectacular
decrease of the ratio of large-perihelion to small-perihelion LPCs with the
shortening of semimajor axis within the range of 5000-100 au is also noticed.
Analysing discovery circumstances, we found that Oort spike comets are
discovered statistically at larger geocentric and heliocentric distances than
the remaining LPCs. This difference in the percentage of large-perihelion
comets in both groups of LPCs can probably be a direct consequence of a
well-known comets fading process due to ageing of their surface during the
consecutive perihelion passages and/or reflects the different actual
q-distributions.
