Thanks for complements.
RCM began making special sets in 1954. (some other earlier sets were also created in 52 and 53, but not like 54,, these earlier sets where a mix of PL and MS grades; or all MS grades..
Charlton started calling these proof like in 1959 as a grading term and grade. In 1962 they created that Proof-Like table we have always seen in the catalog.
The names changed; early proofs became know as Specimen, and in 54 ( I think ) proof-like became the new proof or specimen.
No Specimen coins (or old name proofs) were issued in 1954 to 1968, with the exception of 64,65, and 67. The only specialty strikes were the PL coins.
The Mint had never really mass produced Proof coins or Specimens., (perhaps 1937 counts but still small numbers)
I would image something changing around 1950, and more people asking the mint for early strikes (off polished dies) or looking for these special strikes. By 1954 the Mint is obliging and pumping out special sets.
You can find PL coins in 1953, 52, 51, 50, and even 49 dollars. ICCS use to grade 1949 PL dollars, and then for some reason stopped and decided to either call them Specimen or Mint State. I completely disagree with calling anything PL/SP a MS grade just because. I have a 1949 PL 63 grade coin that really PL. It's not Mint State,, it's really PL.
I can not tell the difference between a 1952 SP65 Dollar and 1952 PL65 Dollar. I think I see "perhaps" a more sharper strike in a SP coin, but generally I'm lost in telling the difference in SP vs PL. Same goes for 1967 SP vs PL. I have a bunch of these and I can not tell the difference unless I'm comparing side by side and even then it's so so small; and even then some coins look like SP in a PL holder and some PL look SP.
PL and SP coins will have a more frosted relief on the legends. (very clean, and very easy to spot) Very hard to do with photos.
New Specimen coins and new Proof coins are completely different again., I quick
ebay search and you can see the difference in mirror relief and frosted relief.
I think 1953 PL is a little special to me because for years we were told there were 300 sets made or 500 sets made, nope 1500 sets, and PL started in 1953 which it didn't.. I too purchased a Mint State set in cardboard thinking it was PL only to be disappointed.
I now have my 1953 PL set!
The dollar is a SWL by the way, and I think that 25 cent piece in unique.