Just in case you aren't aware, you can do online check-in and somebody else could still 'take' your pre-assigned seats before you get there.
This has happened to us on a couple of occasions. Usually, when people show up to do twilight check-in and either haven't pre-booked seats or don't have seats together, they just move other people to accommodate and the fact that you have already done OLCI doesn't seem to matter. Last time we managed to get our pre-booked seats back as they had ended up splitting up our party but they do tell you that there are no guarantees. VA's website states that "To honour this request, Online Check In needs to be completed no later than 13 hours before your flight departs. Whilst we will always try our best to meet your requirements, please note that seat numbers are never guaranteed and are subject to operational changes."