  The Voyagers (V) 1 and 2 Ultraviolet Spectrometers (UVS) data harvest covers
outer planets encounters, heliosphere sky-background measurements, and stellar
spectrophotometry. Because their operation period overlaps with many
ultraviolet missions, the V1 and V2 UVS calibration with other spectrometers
are invaluable. Here we revisit the UVS calibration to assess the intriguing
243 % (V1) and 156 % (V2) sensitivity enhancements recently proposed. Using the
Saturn Lyman-$\alpha$ airglow, observed in-situ by both Voyagers, and remotely
by IUE, we match the Voyager values to IUE, taking into account the shape of
the Saturn Lyman-$\alpha$ line observed with the Goddard High Resolution
Spectrograph onboard the Hubble Space Telescope. For all known ranges of the
interplanetary hydrogen density, we show that the V1 and V2 UVS sensitivities
cannot be enhanced by the amounts thus far proposed. The same diagnostic holds
for distinct channels covering the diffuse HeI 58.4 nm emission. Our
prescription is to keep the original calibration of the Voyager UVS with a
maximum uncertainty of 30 %, making both instruments some of the most stable
EUV/FUV spectrographs of the history of space exploration. In that frame, we
reassess the Lyman-$\alpha$ emission excess detected by Voyager UVS deep in the
heliosphere, to show its consistency with the heliospheric but not the galactic
origin. Our finding confirms results obtained nearly two decades ago--namely,
the UVS discovery of the heliosphere distortion and the corresponding local
interstellar magnetic field's obliquity ($\sim40^{\circ}$ from upwind) in the
solar system neighborhood-- without requiring any revision of the Voyager UVS
calibration.
