M Rob,
I am pretty much in same situation as you, I needed wife application to be linked to my sons for marriage certificate, I’ve been told for 5 weeks now it will be linked up or it has been. Then on Monday it came back in post so i had to resend special delivery. It arrived Wednesday and like you I imagine if sitting in post for a while which will affect upgrade, I am within 14 days on Sunday so I will still try upgrade. One advisor told me i should still be able to upgrade as my sons as original document the birth certificate has been scanned and marriage is only needed to confirm mothers change of name. Keep us updated if manage any breakthrough