Funny you mention this. I just got my JDM legacy windscreen changed as there was a crack from a stone. Done by auto glass and as you mentioned the replacement glass did not have to slot in for the fitting holes. However there was no difference in the length. All he did go get over the replacement glass not having the inserts was he put glue in it. He said they normally don't even do that but i was chatting away to him while he was changing it. He mentioned the glass generally is made and shipped from France for most of the cars. They had my BP5 legacy glass in stock which i was a bit surprised about.
One other thing to keep in mind is that they don't provide the seal around the glass. I got him to take off mine and reuse it as it looks a lot better than the generic rubber he was going to use. Was a cold morning so i got out the hairdryer to loosen it up.