Dictionaries typically tend to list only attested words (etymological dictionaries in comparitive linguistics are different) and some also give a reference for obscure terms.
An example: on page 1437, LSJ gives:
πολυβόλος, ον, throwing many missiles, καταπάλτης Ph.Bel.73.34.
After some searching I found a digitized version of the text edition (in public domain, copyright has expired): https://archive.org/details/philonsbelopoiik00philuoft/mode/2up
The relevant page and line is:
Therefore the ptol_siege_polybolos_packed.xml file should have <SpecificName>Polybolos Katapaltēs</SpecificName>.
As an added bonus (serendipity!), I stumbled on a 2009 article discussing the machine (@Alexandermb): https://core.ac.uk/download/pdf/55030687.pdf