Colt 1991 question

[smle-man]

Looking at a used 1991 via pictures and noticed that the frame rail above the slide stop notch is cut away ala a Browning High Power. Is this an owner modification or the way the 1991 is made? I saw many 1911A1s in late Army service with the rail cracked at this point and often thought that a simple fix would be to just not have the rail at this area.

[smle-man]

To answer my own question it turns out that this is factory original done after problems arose from the 10mm frames cracking in this area.