  Very high-energy (VHE, E\,$>$\,100\,GeV) $\gamma$-ray data are a valuable
input for multi-wavelength and multi-messenger (e.g. combination with neutrino
data) studies. We aim at the conservation and homogenization of historical,
current, and future {VHE $\gamma$-ray-data} on active galactic nuclei (AGN). We
have collected lightcurve data taken by major VHE experiments since 1991 and
combined them into long-term lightcurves for several AGN, and now provide our
collected datasets for further use. Due to the lack of common data formats in
VHE $\gamma$-ray astronomy, we have defined relevant datafields to be stored in
standard data formats. The time variability of the combined VHE lightcurve data
was investigated, and correlation with archival X-ray data collected by {{\em
RXTE}/ASM} tested. The combination of data on the prominent blazar Mrk\,421
from different experiments yields a lightcurve spanning more than a decade.
From this combined dataset we derive an integral baseline flux from Mrk\,421
that must be lower than 33\,% of the Crab Nebula flux above 1\,TeV. The
analysis of the time variability yields log-normal flux variations in the
VHE-data on Mrk\,421. Existing VHE data contain valuable information concerning
the variability of AGN and can be an important ingredient for multi-wavelength
or multi-messenger studies. In the future, upcoming and planned experiments
will provide more data from many transient objects, and the interaction of VHE
astronomy with classical astronomy will intensify. In this context a unified
and exchangeable data format will become increasingly important. Our data
collection is available at the url: {\tt
{http://nuastro-zeuthen.desy.de/magic\_experiment/projects/light\_curve\_archive/index\_eng.html}}.
