You can spend more than that on a safe queen NOS unserviced unpolished perfect example with box and papers or a fraction of that price for a middle of the production beater to wear everyday with abandon. Early dials cost more, last year of production costs more, patrizzi, etc, etc. Just because it's cpo doesn't mean it hasn't been parts swapped or polished to a pebble. It would help to understand more specifics of what kind of 16520 you are looking for and if you don't know then this is a great opportunity to get nerdy before you pull the trigger.
I bought one this spring, prices ranged from about $17k to $40k. I looked at a dozen or so examples, prices and condition all over the place, patrizzi sub dials, inverted six, papers, case back sticker, service papers, etc and one really needs to see multiple in person to start to get a sense of comparative condition. Some were definitely not in great shape but you would never know without having seen a bunch for comparison. For me, I wanted one to wear, not to collect. That meant luminova dial and as close to new condition as possible without paying extra for boxes, papers, etc so not the most collectible but a perfect throwback to the watch I had always wanted when these were new.