what basis you've allocated these to RIC 129 instead of 123?
Weight. 129 is c. 5,2g while 123 is the half (diameter is also different).
Yes, the diameter for 123 is 17- 19mm, while 129 is 21- 23mm
Regarding the freshness of the coins, I assume that they are probably coming from the same find. And so, we can suppose they have been hoarded "just out of the mint".
These coins all came from the same lot I bought from someone in Germany. There were 10 coins in total- 6 were FTR fallen horsemen and 4 were FTR victory steering galley and all that had readable mintmarks were from Thessalonica. I have to assume these were from the same find, as the chances of these coins being together otherwise is unbelievable. Most of the fallen horsemen are also silvered, but my pictures do not show that so well.
Below is the other fallen horseman
Constantius II
A.D. 348- 350
23x25mm 6.3gm
D N CONSTANTIVS P F AVG; pearl diademed, draped, cuirassed, globe in right hand.
FEL TEMP RE-PARATIO; Soldier spearing fallen horseman.
In ex. TS epsilon *
RIC VIII Thessalonica 115