Something like this was mentioned a little earlier:
http://www.iris.washington.edu/pipermail/sac-help/2006-August/000111.html
I didn't see a resolution or much further discussion so
I wanted to point out that while the older version
of sac (00.56a) would throw an error on merging if two
files overlapped or were less than a sample interval apart
(ERROR 1802: Time overlap:), the newer version (100.1)
does not spit any error (on both solaris and linux), does
nothing with the files in memory (that I can tell), and
doesn't halt a macro (so it just keeps on going). It is
somewhat annoying when there is a _gap_ between two files
ever-so-slightly less than a sample interval (like a
millisecond), you go to merge, and nothing happens.
Just something to look out for..
Cheers!
Garrett