Updated Sep 14, 2015 at 10:36a ET
The three Mercedes F1 customer teams are still waiting to see when they will be offered the upgraded engine used by Lewis Hamilton to win the Italian GP.
Mercedes utilized all seven of its 2015 development tokens on the engine, which is actually a 2016 project that it opted to bring forward into this season.
The logistical complication is that it's Mercedes policy to treat all teams equally, so Brixworth would in theory have to make six units available on the same race weekend for the customers, as well as having enough to service the needs of Hamilton and Nico Rosberg.
In addition, the teams would need access to an upgraded fuel spec in order to take full advantage of the changes.
The other issue is that the three teams would have to fit the new engine into their planned usage schedules, without it becoming an extra change.
"We haven't been promised anything at this point," said Force India's Bob Fernley.
"It's a Mercedes decision really. The original decision was this wouldn't come out until 2016, the fact that it's come out now, they may want to extend it to the customer teams.
"It depends what the directive is from Mercedes. I think the answer is to find out from Mercedes what they want to do, and then we'll adjust our program. It just depends where they are in the schedules. We lost an engine with Nico [Hulkenberg], so he's a bit out of synch, but then Nico missed the race in Spa. So we need to look at the whole picture of where we are with engines."
Meanwhile, Claire Williams said the Monza performance gave her confidence that her team would eventually get a boost in its fight with Ferrari.
"It does, towards the end of the year," said Williams.
"There's a development plan in place, so we're having that conversation."
Rob Smedley, head of vehicle performance at Williams, added: "It certainly looked as though it has a bit of pace on it, so we'd love that in our car as soon as we can get it."