I think the idea that Thoroughbred blood did not make it to Hanover until 1850 is probably wrong. You have to remember that the King of England was also the Elector of Hanover from the early 1714 until 1837, a personal union with the British Crown. This is also the time that the TB was being developed in the UK (and the US), and it would take a huge stretch to imagine that a British crown that was so interested in horses for cavalry at home would not be equally interested in such horses in Hanover. King George II of England founded the Celle stud in 1735, and many stallions were imported for improvement by him and his successors. Wikipedia says that King George IV exported 50 of his personal stallions to stand at Celle before 1828. We know he was involved in racing because QEII uses his racing silks.
Just in Alnok’s pedigree there are two TBs, one foaled in 1818 and one in 1828.
Fling has a German ancestor named Oberon foaled in the 1810s who was a grandson of a British TB foaled in the 1780s. Oberon was a Mecklenburger, which seems to have been heavily used by the Hannoverians. Found another TB in Fling’s ancestry who sired a Mecklenburger with two generations of German TB after the British one foaled in 1780. The British sire was imported in 1786 by Gestut Ivenack. That Mecklenburger (Malcolm) was foaled in 1826 by Gestut Ivenack and stood at Celle.