Open and cock the gun; with the gun cocked, remove the forend (as you have done already). Look on the flat part of the fore iron (the part hidden when the barrels are attached). You've already seen the serial number on that component, so look again for a patent date as the auto ejector patent date will be located there as per the photo below; and if so that TYPE II auto-ejector patent will be dated May 28, 1901. But some of the earliest TYPE II auto-ejector guns, those built before the patent grant, might read Patent Applied For; and it's also possible that a lower grade auto-ejector gun like yours built before the 5/28/01 patent grant date may not have an auto-ejector patent reference at all.