IIRC, there was something in the Tallinn sightings about Brian/Ericka being far behind. Maybe they get bad luck at the haybales and end up leaving last, a la Adam/Rebecca every leg?
Even if this is so, I will wager that the at the beginning of the final leg, leaving from Prague airport, all teams will have been equalized by Bunching. As long as they do not get truly "too far behind" it will be OK.
My recollection of the ferry schedule is that it is once a day from Stockholm to Tallinn. If so, I hope that Brian/Ericka make that ferry because if they don't the only non-airplane alternative is via ferry to Helsinki and connecting there to a 2 hour ferry to Tallinn. I remember this as being 5 to 6 hours later in arriving at Tallinn. Depending on hours of operation, that may or may not cause them to get way further behind.