Not really the opposite. I was at simply stating that the additional thing could be returned without problem and that as the OP described the issue, it had been taken but not seized as it was not seen (you can't seize something you haven't seen). This happens all the time where things are taken for the wrong time period (most common mistake with documents - electronic or otherwise), are not as named in the warrant, are third party property found in a common area (such as banking records of another person not named in the warrant) etc.
Sure ) , that would apply to documents and correspondence belonging to other people, as well as to non related things (like a pocket umbrella, a broken keyring, 2x25 cents coins, etc.) but the OP was talking of devices, and specifically of devices capable of retaining data.
I was trying to clear that if the nature of the "things" is a device capable of retaining data and the original search warrant is for "data", there is no way the "things" will be returned to the suspect without some kind of prior examination/inspection and/or some well thought upon decision, to me the "opposite" of "can be returned to the point of seizure without a problem".
jaclaz
There are many cases where they seize a computer which has a CD/DVD left in the optical drive, and they are unaware of the presence of such a CD/DVD, which obviously is not recorded in the list of seized materials.
The reason it is not recorded is because they did not know that there was a CD inside the optical drive during seizure. Had they known, they would have added it to the list. So, just like jaclaz said, since they are after anything that could "retain data" these items must be examined, and not returned unless told to do so by the prosecutor/judge.