Hi, I have such an Epiphone, serial number begining with 88 and I cannot find when it was made either! I would guess the guitar is either a copy or eipiphone had samples made by prospective suppliers in the late eighties. Due to the 88 at the front I think it might be an early sample from the company whom started manufacture in the 90’s for Epiphone. There is one extra digit to many to show it as being in the Gibson series. Except the extra digit is a zero behind the 88. Do the numbers 88 and the last number 5 on your guitar label have a bolder appearance? My guitar is a beautiful natural maple front and sides with a big lump of pinkish wood inside and sounds absolutely great. Hope you can find out more about these guitars. Good luck.