Not entirely true! The Glocks numbered <10 or >50 are the most desirable and command the highest resale price. Those are the investment grade Glocks.The ones with a number. Example: Glock 17.
I am toying with the idea of listing my Glock 7 in the NES private WTS section. I would not list a price but instead would accept the highest offer over the next two weeks. Send Venmo and I'll mail Glock 7 to your FFL for transfer.