Brand & Neck Labels
Do not expect every authentic piece to say Saint Laurent. Historical garments may read Yves Saint Laurent, Saint Laurent Rive Gauche or other era-specific wording; modern ready-to-wear commonly uses SAINT LAURENT PARIS/SAINT LAURENT treatments, while bags and accessories can use the interlocking YSL Cassandre monogram.
Sui Generis approach: first establish the likely era and product category, then compare the wordmark/logo, label construction, typography and placement to documented examples from that same period. A genuine vintage label can be very different from the current retail label.
Brand labels, size tabs and care/product labels should be assessed as a set. For Saint Laurent, expected construction can change by line and era, but the label materials, edge finishing, stitch attachment, printing/weaving quality, fiber/origin information and wear should be internally coherent.
A label that looks older than the garment, a pristine label on a heavily worn item, a care label whose language/fiber data conflict with the garment, or obviously re-sewn label stitches are reasons to slow down. Alterations can move or remove labels, so document tailoring evidence before concluding the label was transplanted.