  The recently published Yemeni observing report about SN 1006 from al-Yamani
clearly gives AD 1006 Apr $17 \pm 2$ (mid-Rajab 396h) as first observation
date. Since this is about 1.5 weeks earlier than the otherwise earliest reports
(Apr 28 or 30) as discussed so far, we were motivated to investigate an early
sighting in more depth. We searched for additional evidences from other areas
like East Asia and Europe. We found that the date given by al-Yamani is fully
consistent with other evidence, including: (a) SN 1006 "rose several times half
an hour after sunset" (al-Yamani), which is correct for the location of Sana in
Yemen for the time around Apr 17, but it would not be correct for late Apr or
early May; (b) the date (3rd year, 3rd lunar month, 28th day wuzi, Ichidai
Yoki) for an observation of a guest star in Japan is inconsistent (there is no
day wuzi in that lunar month), but may be dated to Apr 16 by reading wuwu date
rather than a wuzi date; (c) there is observational evidence that SN 1006 was
observed in East Asia early or mid April; for the second half of April, a bad
weather (early monsoon) period is not unlikely -- there is a lack of night
reports; (d) the observer in St. Gallen reported to have seen SN 1006 "for
three months", which must have ended at the very latest on AD 1006 Jul 10,
given his northern location, so that his observations probably started in
April. We conclude that the correctly reported details give quite high
confidence in the fully self-consistent report of al-Yamani, so that the early
discovery date should be considered seriously.
