France 1927 Airmail Overprint "Merson"?

Looking for information on the types of this overprint & their features.
Some auction houses say Series 1 others Merson Type

The two overprinted stamps are called Type Merson, because Luc-Olivier Merson was the designer. His design was used for several denominations, which were released in 3 series:
1st series (1900) - 40c, 50c, 1f, 2f (violet), 5f
2nd series (1906-20) - 45c, 60c, 2f (orange)
3rd series (1925-26) - 3f, 10f, 20f
So the 2f (orange) overprint is from the 2nd series, and the 5f is from series 1.

This site shows all the stamps Type Merson:

http://www.coppoweb.com/merson/france/fr.40c.php

For a history of the 1927 overprint see here:

http://www.stamp-collecting-world.c...s_1927a.html

Here is a site describing how to check forgeries of the overprint:

http://www.richnoddystamps.co.uk/fo...ris-airmail/

22Crows - Thank You - Should be all I need