Vintage crochet and knitting patterns often have information different than modern patterns. Abbreviations were common since most vintage patterns were written out, most did not use charts or diagrams as modern patterns do. The crochet hook and knitting needle sizes might also be sized differently. The yarn called for may not be available since the patterns are decades old so the chart should help to find a suitable substitute.
Digital vintage crochet and knitting patterns call for vintage yarns that are most often discontinued so information about the yarn used helps to find a current yarn to substitute. I always recommend doing a gauge test before starting to be more certain.