I don't recall any B/W crts larger than 23" (approx 21"/but with squared corners) that had the square corner shape. there were 24" and 27" sets offered in the waning days of B/W sets but IIRC, these had the more rounded corners like this spectacular Zenith 27 incher:
http://tvhistory.tv/252KA21A5.jpg
From TV history site.
jr