about /oi/ > /u/

I searched a bit trough the Thracian glosses for seeing if there is
something to find about this change. There is something to find , the
value of that what I found should be appreciated better after one
will be able to verify how chronological these mentions appears. I
let open for you any considerations about this /oi/ > /u/

River Oeskus appears mentioned as:

Oiskos, Oeskus, Uskus.
Beside of this , Uskudama , the old name of the Odrysian city

The "Thracian Hero", Ouetespios appears mentioned as:

Ouetespios, Outaspios, Utaspios

Dacian King name Roimetalces appears mentioned in three forms:

Roemetalkes, Roimetalces, Rumetalkes,

The Dacian plant "kinuboila" appears mentioned in two forms:

kinuboila, kinupula

The whole material here has been extracted from the work of Cicerone
Poghirci appeared in 1976 with the title "Trace et daco-mésien:
languaes ou dialectes?".

Alex