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And sometimes guns shipped directly to a Spanish military or police organization weren't proofed, perhaps on the theory that the military would do its own testing of the product before acceptance, something not practical for civilian customers.
So, with the understanding that sometimes there were no proofs at all, the usual places for proof stamps on 900 Series guns were - • A pair of single proofs on the right side of the barrel and barrel extension, on either side of the joint between the two.
) 1944 → O 1945 → P 1946 → Q 1947 → R 1948 → S 1949 → T 1950 → U 1951 → V 1952 → X ... Note that although the year codes start with A, that by itself is not evidence that these codes were actually in use by 1927.
Actual observed marks on actual observed guns suggests that the year code system was not in universal use that early.
So, just when did the Eibar proof house switch from the older stamps to the newer ones? Guns proofed in 1928 might have either the older or newer stamps.
Of course dating the older stamps can be an exercise, as they don't have a date code.
The two triads above are the only ones I've yet seen (although I have seen the late triad with the same stamps but in a different order, on several specimens of the Astra Model E - and if I had a decent photo, I'd probably count it as a third triad).
In theory there could be some overlap of symbols - a triad composed of, say, the early crowned saltire couped ( 1927 → A 1928 → B 1929 → C 1930 → CH (the digraph CH has been considered a letter in Spanish since 1803) 1931 → D 1932 → E 1933 → F 1934 → G 1935 → H 1936 → I 1937 → J 1938 → K 1939 → L 1940 → LL (same story as CH) 1941 → M 1942 → N 1943 → Ñ (watch out, most lists in English miss this - N and Ñ are different letters!
Antaris describes it as so - "Early Eibar House Proof. But it unquestionably appears on auto pistols made before 1929.
In 1927 it was replaced by the year code." The "early Eibar house proof" Antaris cites is . It did not disappear immediately when the year code was introduced in 1927. However I have seen guns with the early triad (including the P. stamp rather than the date code stamp) which were made after 1927.