Randall D you are correct the SR9c comes with 2 bases for the 10 round mag "It comes with two magazines that provide options in both capacity and grip size. The standard magazine holds 10 rounds and features a flat bottom butt plate; ********a finger grip extension floor plate is also included. The second magazine features a grip adapter and holds 17 rounds, instantly transforming the smaller, compact grip into a full-sized 9mm grip.

James mine came with the pinky extension (uninstalled) I use the pinky extension on mine even the replacement 10 round mags comes with both base plates
UPC: 736676903696 Features and Specifications:
Manufacturer Number: 90369
Ruger factory magazine
Caliber: 9mm Luger
Capacity: 10 Rounds
Body Material: Steel
Spring Material: Steel
Follower Material: Polymer
Baseplate Material: Polymer
Finish: Matte Black
Fits:
Ruger SR9c Compact Pistol
Includes:
********Both Flat and Extended Polymer Base Plate budsgunshop.com/catalog/product_info.php/products_id/81758/ruger_90369_sr9c_magazine_10rd_9mm_w_extension />

Randall, my pistol was purchased locally about 2 years ago and mine did not. Since I remember the box not being sealed, my local FFL could very well have removed it if it was included. I appreciate your response/clarification as it will help other community members, Cheers!