I've always found the way Libreoffice uses to manage Calc files as data sources a little too complicated.
Each time I need a number of entries to feed a Writer doc, I must register a new database, which is undesirable most of the times.
A small trick would be to create a "dummy" database to link to the right Calc spreadsheet.
This is easily done: once you have registered your database linked to its first Calc sheet, it can be modified also starting from Writer:
- press F4 to display available registered databases
- right click on your dummy DB and choose Edit database file
- via Edit -> Database -> Properties where you can choose the source file
It's even possible to change the connection type, that is other kinds of source can be used also, not just Calc sheets, but I've not tested it yet; anyway there are no reasons to think it won't work!