Hi Chris,
Yes, that is completely normal. Unless he uses hand chisels, his router duplicator cannot cut into the tight corners so he leaves it undersized for you to hand inlet. That is how it should be unless he has the CNC multi-axis machinery that Kibler uses, which none of those guys have or could afford to have. If the barrel fits well and the back of the bolster will butt against the back of the mortise when fully inlet, I would be happy with that job. Most kit guns, other than those by Kibler, come like that.
dave