OK, CN1 is very definitely on the "top" side of that board, which I would have called the "less populated side with fewer components" side. If they want to call it the "component side"...I'll call mine "Bob".
Anyway...I took a long slow and repeated look with jeweler's glasses and didn't see anything marked IC13, but the manual calls that the CPU so I presume it is the unrivaled big Toshiba chip on the board. Did look between the ribbon cable connector (ain't plain English grand!(G) and that, no sign of a part marked D17 or any stencil of D17, although there are two solder spots next to a '474' device, in what might be the right location. If D17 used to live there, it ran left-to-right, oriented side-to-side in the radio, but the manual seems to indicate it should have been up-and-down, i.e. parallel to the antenna?
The instructions I've found here and online all say there's a D17 in the US market models, and that reference to a "(N)E" should mean (N)orth American market, no?
It is possible that the radio is just locked out of self-programming because of a software setup, and that I couldn't run the software because of legacy issues, i.e. the Windows programming software is 16-bit and I'll need an older (not 64-bit) system for that to operate.
On the bright side, I did find and remove a tiny thin solder hair from the board, which eventually could have popped free and shorted something out. (Signs of a previous visitor again.)