Grga: Congratulations on discovery of your TIGRA! You are justified to brag about sitting on the edge of what sounds like a veritable treasure trove: please continue to share your bikes with the CR List.
I recently purchased an apparently identical Tigra, with exception of some variation in decals and the crank set (mine is a G.S.). Also, mine (1970) is marked a 'Professionnel.' I agree with you about how difficult it has been to find information about the brand, but which still is in existence (buried inside Trek/Villager) and has or had a racing team. I am more than 3/4 finished with a complete refurbishment, and I will share photos with the list when it is complete.
The placement of the 531 Forks decals seems odd, as one would expect them on the fork blades, only. When I sanded my bike for a re-spray, Reynolds was clearly stamped on all tubing.
You can witness two examples of original Tigras on speedbicycles.com: one (1956) is excellent, the other (1970) is mine (then quite rough).
Good luck,
JB Froke
Pebble Beach, CA