In the 1970s, there were 30 AM stations licensed to Mexico City but I saw no FMs listed! They were as close as 20KHz apart!
Even in the later 60's there were a few independent FMs in Mexico City, several being supported by subscriptions to their SCA music services for storecasting. And many of the AMs had FMs with lower power that were used as STLs to the transmitter site.
I was offered the PD position in 1970 to take the Organización Radio Centro FMs to independent formats with a new transmitter site on top of the Torre Latinoamericana. I chose to go to Puerto Rico instead.
All through Latin America there are local AMs with 20 kHz separation. In the 60's I owned both 570 and 590 in Quito, Ecuador, and there were stations on 550 and 610 as well... the same up the dial with the others either 20 kHz or 30 kHz apart:
550.670,590,610,640,670,700,720,740,760,785,805,835,860,880,900,920,940,960,990,1020,1070,1090,1111,1040,1060,1080,1210,1245,1280,1310,1330,1360,1380,1410,1430,1460,1490,1520,1550,1570. 41 local AMs in one market.
Similar situations were seen in nearly every other country, from Guatemala to Perú. Only Chile, Argentina, Brazil and Uruguay seemed to be closer to the NARBA standard as they were coordinated by a similar pact.