Maurerfreund (a manufacturer) originally released a 0.5mm blade x 5" in width. Reduced to a 0.4mm - this was sold by Refina, not designed or produced by them. This was in 2010 (approximately - as Maurerfreund only established that year)
Storch in Germany had a flexible trowel made for them in 2008....
NELA basically joined forces with a manufacturer in Germany (who made for Storch) and started producing their range. The flexible trowel NELA first brought out was 0.3mm x 4.3" - very different to any other in the U.K. but the same spec to what was sold in Germany, Netherlands and Belgium. The company they joined with had been making flex trowels for years before.
Just because one company introduced them to the UK before another doesn't mean they were the first in Europe.