How do I authenticate a vintage Louis Vuitton handbag?

[mpr1467]

Hi

I have been fortunate to find what I believe to be a genuine Louis Vuitton handbag, produced pre 80's though as there is no serial number tag in the inside pocket.  However, there is some loose stitching in the pocket where the serial number label would normally be, just no label attached.  

In all other respects, the stitching, hardware, leather used, finish inside and out, symmetry of the pattern, all tick the boxes of a genuinebag.  There is a label attached around the base of the handle, with a small, cream, round button, monogrammed with the 'LV' logo  which is printed with the fibre content of the bag, the model number (M51147) and an additional 'LV' leather label.  It all looks good to me, very very good, so if it is a fake, it's one of the best I've ever seen and I know my way round a good handbag!  I think I just can't believe my luck at finding such a gem. Any thoughts or advice?  Many thanks