That is an assumption . It could be called that any time after Larisch took command . There are several examples of various national units maintaining names for hundreds of years .
In various nations - that certainly can be true.
But not with Old-Prussian Regiments, since there the regiments were named after its current commanders.
This is at a time when some units were equipped out of the pocket of the CO . I think I have adequately shown where several units did employ this type of button hole, and while I accept that this does not mean the Larisch had this type of decoration, for the 26th to be famous for it suggests it is at least typical of the Larisch unit if not the army . How else do we explain that at a later date they employed it claiming it to have come from this period and this unit ?
Since at least 1713, the (Old Prussian) regiments weren't equipped out of the pocket of the CO but centrally - from the "Königliches Lagerhaus'.
The (26th Regiment) von Larisch Regiment
) was just the patron for the ... 'Larisch style'. Which is historically wrong, because it should be von Kleist style
. (See my above post.)
And: this style (and the name for it) was used after 1806, with uniforms of the new formed Prussian army (aka 'New Prussian Army' [from 1814 until 1918]).