ADD BOOKS is the only way. The books are fine. The number are part of the DB's method for matching entries FOR THE LIBRARY THEY WERE MADE FOR.
OK, I sorta lied (about the Only part).
IF and Only IF you copied the
entire Library folder to that stick (there will be a
metadata.db file if you did it correct).
Simply attach the drive: right click the Library Icon: Switch/Create: USE EXISTING:<point it to the stick drive folder that had metadata.db>:
If you did this correct, you will see the old Laptop Libraries books.
Select books you want to
merge into you main: Right-click: copy to Library (optional mode) <main one>.
FWIW I use this all the time on a HARD WIRED network to PULL from the laptop. (Pushing from the laptop is unreliable. Using WiFi in the mix, is another problem area to avoid. WIRE has no delays
)