This portepee is technically correct for this model bayonet & you are correct in mentioning that the portepees for the fire bayonet changed. Essentially, there were two types of fire bayonet which were identical with the exception of blade length, the 25cm blade was for lower ranks & the 20cm blade was for officers & NCO's.
The 25cm model, known by collectors as the long model, originally had a silver bullion & carmine knot with black leather strap with 3 rows of aluminum thread in it. The 25cm model, known as the short model, originally had an all silver bullion knot with with the same, black leather strap with 3 rows of aluminum thread. This knot is identical to one type of Army knot except that the cat's anus has a red dot rather than grey or the occasionally seem black.
After the Feuerwehr was assumed into the greater Polizei, they essentially became the Feuerschutzpolizei & as part of the Polizei, adopted Polizei knots. The long model with correctly have the silver/green knot & the short model would have the knot shown in your pics.
As an aside, your pics come from Paul Hogle, Lakeside Trader. Paul is a dealer with an excellent reputation which I believe is well deserved. Anything you buy from him is above reproach & will allow you to sleep easy at night. Hope this helps.
Noticed a typo. In the discussion of pre-assimilation Feuerwehr knots, the 2nd bayonet I spoke of has a 20cm blade (not 25cm) & is referred to as the short model. Sorry for any confusion.