Victor Musical Smart Set P 148 "Glenn Miller: An Album of Outstanding Arrangements on Victor Records", consisting of Victor 20-1564, 20-1565, 20-1566, 20-1567.
Either the factory had some old pressings left over, or your dad had sides 5&6 break at some point and replaced them with an older copy he found elsewhere.
Xiphi, I got these disc photos from my dad's album. He was the original owner, (1940's). I can't explain why two of them are Victors, and the rest are RCA / Victor. But, all the #'s seem to flow in proper sequence, and they all have the P-148 album # on them. (another thing to research)
The only cover I have and which I've now uploaded does not belong to the actual 1944 Victor release (although it looks very similar), but is a later repressing, RCA Victor P-148. The biggest difference is that RCA Victor is mentioned on the back, and there is no listing of Victor Musical Smart Sets on the inside.