"A limited number" is just an assumption, and depends anyhow on how one defines it. The Kokon Kaji Bikō gives rankings for 1,111 smiths, and lists many more, which I personally wouldn't call a "limited number." There are also quite a few "big names" of the Kotō period included; in other words: famous smiths were tested, but maybe not famous heirlooms such as Meibutsu. There's even a report about a Masamune tested, but it failed the Wazamono ranking. No one would argue that this failure resulted in discount prices for Masamune blades .
And finally: *Ryō-Wazamono* is kind of a "modern" reading, the correct reading is *Yoki-Wazamono*.
IMHO I think Nagayama speaks about the blades which were tested by Yamada himself.