There are a lot of monitors that are Amiga compatible that weren't made for the Amiga. Once, there were a lot more. If I remember right, the old CGA graphics on MS-DOS/Windows machines used to require monitors that scanned down into "native" Amiga ranges. With the advent of EGA, then VGA and SVGA, monitors didn't need to scan down that far anymore.
So it is quite possible that you have found an Amiga compatible monitor that doesn't have a 23 pin connector. Since most of these old monitors weren't made for Amigas, they usually won't have a 23 pin connector. Some of these monitors have speakers, most don't. Back then, sound cards for the MS-DOS/Windows machines were in their infancy, so sound was handled with a speaker inside the computer that bleeped and blooped. With sound like that, it was widely held that monitors didn't need speakers. Some of the old monitors (with speakers) even had television tuners so they could be used as televisions. (This was way before TV tuners were included on video cards.) Many companies once made monitors that scanned low enough to be used with Amigas (NEC, Princeton, Viewsonic, Sony, etcetera).
I have an old NEC Multisync II that scans down to 15.5 KHz. It has a 9 pin D connector. I had a custom cable made for it by Redmond Cable Company ("The weird cable company...") to use it on my Amiga. I recently replaced it with an NEC 3D that scans down to 15 KHz. It has a 15 pin HD connector. I use the Commodore 23 pin to 15 pin adapter (part 390682-01) to use it on my Amiga.
So while I can't exactly help you identify which monitor you have, nor can I list the dozens of Amiga compatible monitors out there (especially since I don't know them all), I can tell you that just because it doesn't have a 23 pin connector on the back doesn't mean it can't be used with your Amiga. If you can find a way to connect it, it very well could work.
For what it's worth....