Do you lose your seat reservation if the stock changes?

[signed]

I booked a seat reservation in First, on a weekday Avanti 0902 Euston-Holyhead, which, before the timetable change, was shown as a 805 stock on the seat planner, and therefore I got coach K (only First carriage at the time).

I learned through the forum that 221s will continue to operate that service, and looking now, indeed the seat planner clearly shows a 221, but coach K is nowhere to be found, coach E instead being the First coach.

Do I need to get a new seat reservation? Or can I just expect to have my seat reservation switched to coach E?

 

[30907]

The train still appears to run as 10 coaches through to Holyhead, so I would expect coach K still to exist and I doubt your seat will be transferred.
It's possible that K is now fully booked, but to be safe I would recommend changing your seat yourself (I assume you use the GWR website which doesn't charge, unlike Interrail?).

 

[signed]

The train still appears to run as 10 coaches through to Holyhead, so I would expect coach K still to exist and I doubt your seat will be transferred.

I don't know what's up with the Avanti seat map, which definitely, even in Standard, shows that only 5 coaches are to go to Holyhead

but to be safe I would recommend changing your seat yourself (I assume you use the GWR website which doesn't charge, unlike Interrail?)

Indeed, I used GWR website the first time, then phoned Avanti to amend that and get a solo seat on the 805s (that were planned at that time), where they were very helpful to get me a specific seat.

With the stock change, I called them to get a new reservation, which I painfully got because that agent was very far from helpful. I got it on coach E.