How can I tell if my vintage YSL bag is authentic?

its from the 80s, i guess. It is black leather and has patchwork on the front, with a “ysl” badge on the front. It doesnt have any tags. On the inside it says “Yves Saint Laurent” and “Paris”. and underneath the metal button it says “UK Pat” and then a long number. then it says “uk and d973664″.

yep

Vogue 2036 Sewing Pattern Paris Original Yves Saint Laurent Jacket Skirt Shawl Size 8 – 12 Semi-fitted, interfaced, lined, hip length jacket has collar, shoulder pads, side panels, no side seams, welt pockets and long, two-piece sleeves with button vent. Semi-fitted, slightly tapered, lined skirt, above mid-knee, has waistband, front tucks, side front pockets, side zipper and back slit. Double layered shawl….

Lanc¿me Fatale Exceptional Volume Sculpting 3D Comb-Mascara, Black 0.23-Ounces $20.44 Sculpt your lashes with exceptional volume. Unique Ampliform 3D Comb coats and sculpts with one dip and a single stroke….

Paris By Yves Saint Laurent For Women. Eau De Toilette Spray 2.5 Ounces $35.51 Paris by Yves Saint Laurent: a seductive scent for the elegant woman, who embodies a modern romance. A radiating accord, which expresses all facets to the rose. A blooming fragance of May rose – sandalwood….