When an EPUB has no EPUB 3 belongs-to-collection / group-position properties, KMServer falls back to the OPF 2 <meta name="…" content="…"/> form for the series title and the book’s number/numberSort:
calibre:series/calibre:series_index(calibre)- the bare
series/series_index(common in fan-packed light-novel EPUBs)
The Java version only reads the EPUB 3 property form.