Why Is 1948 Dime Considered Key Date?

"Key Date" is one of those numismatic terms like "rare", or "scarce" that sellers use to hype their wares.
Usually it refers to the coin in a series with the lowest mintage and highest value.The 1948 dime,with a mintage of about 400 thousand,is the lowest in its series and has a relatively high price in lower grades,in higher grades the 1938 fetches a higher price due to grade rarity, so the "key date" in this series depends on what you are selling.

Anybody can call any coin a "key date" but that doesn't make it so.
It's often misused by sellers trying to hype their wares, IMO
The minting of 1948 Canadian coins began late in the year because they had to wait for new dies omitting the reference to India.
The 1947 ML (Maple Leaf) coins were struck in the interim.
Check the Charlton or Haxby catalog for exact mintages.

Perhaps the mintage speaks for itself, however, I don't know about anyone else, but I have had a difficult time acquiring this date in high grade. My entire King George VI dime collection is currently I.C.C.S., MS-65, however, my 1948 dime is only an MS-64.
Ironically, when viewing the 2012, I.C.C.S., Population Report, the 1948 dime has one of the highest mint state available pieces up to MS-64, but fewest in MS-65.
Over the past 10 years I've had less than a hand full of opportunities to upgrade to an MS-65 but have been unsuccessful each time! So this would be my opinion as to why the 1948's a KEY!

Glenn