Vintage Chanel

Hi all!
I got a vintage medium full flap chanel Lambskin from Rebag earlier this week. It showed up yesterday and from the posts I have seen I am getting it authenticated by Zeko. After going back and forth it seems that the bag and its serial number do not match- the bag is from the mid 80s but the serial number is in the early 1990a and she says the interior of the bag has been replaced and in order to issue a certificate i would need to remove the serial number sticker from inside . This feels like odd advice, so wondering if anybody else has experienced this?