I would direct your question to Steve Preston (stevepr@...), since
he has a better understanding of the processes involved and generates
the predictions shown on his website. I am mainly the total/graze
occultation guy for lunar/stellar events. I do know that updated
astrometry has shown path shifts in past events. He usually obtains
the astrometry a week or two before the actual event. The website now
is getting into the first few weeks in July with recently updated
events.

--- In guide-user@yahoogroups.com, "toadatrix" <jsnyder@w...> wrote:
> Thanks. I downloaded the new Tycho2 and other catalogs listed below
> and that solved my problem about Occult not finding the Sept 5
> event. The new data matches the Guide8 predictions pretty well,
> showing the occultation path in NW Wisconsin rather than SE
> Wisconsin (the latter being the Sky & Telescope location). Should I
> assume that, at least for now, the best prediciton is that given by
> Occult and Guide8 which both show the path in NW Wisconsin? In
> other words, is the predicition of an event visible in SE Wisconsin
> as published in Sky & Telescope now less considered less likely?
>
> --- In guide-user@yahoogroups.com, "sc285" <rob515@k...> wrote:
> > I placed in the files section of the group, the Goffin Planetary
> chart
> > which gives general information and locator charts. Steve Preston
> > maintains the IOTA Asteroid occultations, and his website is
> located
> > at: http://www.asteroidoccultation.com/
> > Since astrometry closer to the event can actually shift the path,
> the
> > article in S&T gives general information, but that can change.
> >
> > Incidently there is a NEW version of the Tycho2 catalog for Occult.
> >
> > Denis V. Denissenko wrote:
> > "The cause of problem was identified - wrong order of stars in
> several
> > regions in Tycho2.dat. To make long story short, stars *were*
> there,
> > but WinOccult was *not* finding them because they were not at their
> > places.
> >
> > I have completely rearranged Tycho2.dat in the correct order and
> also
> > recompiled tycho2.inx file. There are still all the same 3375961
> stars,
> > but now WinOccult is finding by 3-3.5 per cent more occultations!
> > Especially in Gemini, Auriga and Taurus between declinations of
> > +23.5..+24, +24.5..+25. +26.5..+27, +29.5..+30 and in Capricornus
> and
> > Aquarius at -2..-2.5 and -5..-5.5 bands. These are the results of
> my
> > test with occultations of stars brighter than 10.5m in 2005.
> >
> > The fixed version of Tycho2.dat and tycho2.inx is uploaded at
> > http://hea.iki.rssi.ru/~denis/TychoNew.zip (64.264.832 Bytes, or
> 62758
> > kB). Perhaps it will be desirable to upload the replacement at
> IOTA ftp
> > site after additional testing by Dave Herald and one or two
> > calculators. If you have some downloading software like Download
> Master
> > or something like that, please use it rather than simple "Save as"
> from
> > your browser. File is too large, so it might take several
> attempts."
> >
> > David Herald (author of Occult) wrote:
> >
> > I'm very happy to advise that I have now done a series of checks
> on the
> > files that Denis has re-created, and they are fine.
> >
> > Denis - thanks for the great work in fixing up this bug.
> >
> > Rob - can you upload the files from Denis' site, and put them on
> the IOTA
> > site with some explanatory notes. Main guidance - the new files
> > required are
> > Tycho2.dat, Tycho2.inx, and HipparcosIndex.dat - and these simply
> replace
> > the existing files of that name in the StarCats directory.
> >
> > Dave H
> >
> > The file is also located at the IOTA FTP site:
> > ftp://lunar-occultations.com/pub/
> >
> > More detailed information can be found on the Occult Yahoo
> discussion
> > group archive located at:
> > http://groups.yahoo.com/group/occult-software/
> >
> >
> > Rob Robinson
> > VP of IOTA Occultation Services
> >
> >
> >
> > --- In guide-user@yahoogroups.com, "toadatrix" <jsnyder@w...>
> wrote:
> > > I discovered that for some reason, I don't know why, the Tycho 2
> > > star 5244-0017 is not in the Tycho 2 catalog supplied with
> Occult.
> > > It is in Guide8 so I used the Guide8 position of it and added it
> to
> > > Occult. I then recomputed the occultation using Occult and the
> > > reported times and occultation path are similar to, but not
> exactly
> > > the same as, those shown by Guide8. Both Guide8 and Occult show
> > > paths for this event that are well to the north and west of the
> path
> > > shown in the March, 2004 Sky & Telescope.
> > >
> > > --- In guide-user@yahoogroups.com, "toadatrix" <jsnyder@w...>
> wrote:
> > > > According to the March, 2004 issue of Sky & Telescope (page
> 103,
> > > > 106) the asteroid 107 Camilla will occultate the 11.8
> magnitude
> > > star
> > > > TYC 5244 0017 on Sept. 5, 2004 at around 9h UT. The map shown
> on
> > > > page 103 shows the central path passing over the southern part
> of
> > > > Wisconsin where I live. I calculated the same event in Guide
> 8b
> > > and
> > > > found the central path missing southern Wisconsin all together
> and
> > > > passing, instead, over the north west corner of Wisconsin.
> > > >
> > > > Since Guide has always been dead on accurate for me I have to
> ask
> > > > what accounts for the difference and which prediction (if any)
> may
> > > > be correct? I should mention that I also tried to find this
> event
> > > > with the latest version of Occult and I couldn't find it at
> all
> > > > (that was really surprising). Is there a way to get the
> latest
> > > > information into Guide so as to get the most accurate
> > > predictions?
> > > > Where would I go on the web to get that latest information?
> > > Thanks.