Drilled Holes Behind Skirting Boards?

[Tom_Sauce]

Hi all,

I've recently removed some skirting from an extension that runs along the old exterior wall.

Behind the skirting along the length of the wall are lots of drilled holes.

These look like the type you would see if cavity insulation has been sprayed in or maybe they have been drilled for some other reason, I haven't a clue ?

As the skirting was an odd size I want to plaster over the bare brick and these holes to get a better finish to place me new lower skirts on.

Do you think that would be ok? I'm wondering if they have been drilled for ventilation of the walls maybe?

Thanks for your help