Earlier, I wrote
French, Spanish, and Italian sellers may follow the Yvert & Tellier or Michel listings. So, they may offer the 1925 stamps separately. But will you, actually, get the correct set of stamps? I am not convinced you will.
I find sellers from these countries rarely state the watermark or show the back of the stamps. I contacted some that did not know there exist two watermarks. I, frequently, see that where the seller posts a picture of the back of the stamp, the watermark is not the one mentioned in the listing. I have seen listings of more than one stamp that mixed the watermarks.
I frequently come across listings that mention an Yvert & Tellier catalogue number but list the period 1917 – 1932. The first overprints in French currency were issued in 1917. These were overprints on stamps with the 'Royal Cypher' watermark. The concurrent high value stamps were the 'Seahorses.' The year 1932 saw the issue of the highest value stamp with overprint in French Francs, 6 Francs on the Bradbury, Wilkinson printing of the five shillings 'Seahorses' stamp. The overprints on stamps with the 'Block Cypher' watermark were released to the public in 1924 and 1925. Two further values were issued in 1934.
Unless I am mistaken, Yvert & Tellier lists the 25 centimes on 2½d blue with 'Royal Cypher' watermark as number 5. It lists the same value on 'Block Cypher' watermark as number 15. Any listing that refers to 1917-1932 may refer to the original stamps, with 'Royal Cypher' watermark and the two 'Seahorses' stamps. It may also refer to any of these stamps, other than the new values issued in 1934 without discerning between watermarks. In the latter case, does a reference to Yvert & Tellier nr. 5 mean the stamp has the 'Royal Cypher' watermark? Or did the seller not bother to check the watermark and could it be an Yvert & Tellier nr. 15? The former are priced a little higher than the latter in my 2007 SG 'Empire' catalogue.
I asked a few sellers on Delcampe who either did not identify the stamp at all or listed it as Yvert & Tellier nr. 5 for a scan of the back of the stamps. In most cases such a scan will show the watermark. One seller who offered an unmounted mint block of four Yvert & Tellier nr. 5 stamps at € 3 replied by posting a scan of the back of the block.
They were the missing 'Block Cypher' Yvert & Tellier nr. 15 stamps.