ah, many of these things have happened to me like
not finding an specific cel when going through my
collection (most of the times because the cel was
placed together with another) or leaving it on the
scanner bed (this happened to me twice).

Now for my own safety i place all the cels from
the same series together so if i have to look for
one it's easier to look for the whole pack of cels
of the series and then do a more deep research
within there.

Of course this doesn't make sure that it won't
happen again.... Even now i have it easier to find
cels i know it can happen again in the future