Do Sync profile speeds on FTTC connections vary over time?

[#1]

I have had my FTTC connection for the past month, syncing at 78mbit according to the plusnet site and the email i received 2 weeks after being active. however at the weekend it dropped by 5mbit for some reason, it still shows as 78mbit on the plusnet page (https://portal.plus.net/my.html?action=data_transfer_speed although im not sure if this is live?) but on the bt wholesale page it shows an IP profile of 72mbit...
real world speed tests before were 74mbit, now they are 69... now I completely realise that 69 is still fantastic, but... it's been 74 for the past month so i'm just wondering if the sync rate will fix itself? do the profiles go up and down by themselves?
thanks (i did log a support ticket a couple of days ago and havent heard anything back, but i suppose it's not exactly high priority, which I agree)
thanks!

[#2]

Hi Xtigma,
I've taken a look over your connection and cannot see any issues, you've had a re-sync at slightly lower speeds. I see you've tried a power cycle to no avail.
It would be a case of monitoring your connecting and see if it picks back up as the sync speed can differ from time to time and you're currently well above your estimate.