I recently bought not 1 but 3 Birkins, one was new...a facebook challenge with good results.
Two were almost vintage, from the early circle stamp and no stamp days, HAC type.
I learnt that aftercare service was IMPECCABLE and customer was king, not brand.
Two....the bags were made well enough to last 200 years plus easy...and more if "serviced"...called the spa.
The really gool Barenia leather...these were special.