Structural integrity

[FrankCrank]

....the holes may be there to allow hot gases to escape during the welding process....

 

[fossyant]

Holes at the end of stays were usually there for gasses to escape when braising the frame. Ones in the middle, well that's me baffled for a reason, but for aesthetics, I'd get them filled, or braised before a repaint. Won't affect the bike. The BB area looks pretty clean inside the frame - (no rust).

 

[Paulus]

After looking at the drilled holes, there are no cracks radiating from them, so that indicates that there is no stress at that point. Looks a nice frame.