jib71 Thanks for the advice above.

Just to update based on our experience in London this week:

My girlfriend went to Collinson at St. Pancras around 6pm on Sunday, which was about 68 hours before her OSL-HEL-HND on Finnair/JAL itinerary started. Asked them nicely if they could process it ASAP as she needed it ideally by the next day, and they wrote URGENT on it and said no problem. Went back on Monday morning after they'd emailed the PDF results in order to pick up the filled out Japanese/English MOFA form. Then she later realised they'd made a mistake (put nationality as UK instead of JP), so went back in the afternoon to get the form re-issued. Tuesday, uploaded the MOFA form and vaccination certificates into MySOS and flew to Oslo on a separate itinerary. Wednesday morning, MySOS was green, and the Finnair check-in agent asked to see the PCR results (showed the paper MOFA form), digital vaccination certificate, and the MySOS app too.

On arrival, since it's post June 1st, she won't have to do a test and I'm not sure if she'll even need to show anything other than her passport.